Document:

Dated as of March ____, 2012

 

MDB Capital Group LLC

401 Wilshire Boulevard

Santa Monica, California 90401

 

ClearSign Combustion Corporation

12870 Interurban Avenue South

Seattle, Washington 98168

 

Ladies and Gentlemen:

 

This agreement is being
delivered to you in connection with the proposed Underwriting Agreement (the “Underwriting Agreement”) between
ClearSign Combustion Corporation, a Washington corporation (the “Company”), and MDB Capital Group LLC (“MDB”)
relating to a proposed underwritten public offering of shares (the “Shares”) of the Company’s Common Stock
(the “Common Stock”).

 

In order to induce MDB
and the Company to enter into the Underwriting Agreement, and for other good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the undersigned agrees that, during the period beginning on and including the date of the Underwriting
Agreement through and including the date that is the one year anniversary of the date of the Underwriting Agreement (the “Lock-Up
Period”), the undersigned, or any affiliated party of the undersigned, will not, without the prior written consent of
the Company, directly or indirectly:

 

		(i)	offer, pledge, sell, contract to sell, sell any option or contract
to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend or otherwise transfer
or dispose of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, whether
now owned or hereafter acquired by the undersigned or with respect to which the undersigned has or hereafter acquires the power
of disposition, or 

 

		(ii)	enter into any swap or other agreement, arrangement or transaction
that transfers to another, in whole or in part, directly or indirectly, any of the economic consequence of ownership of any Common
Stock or any securities convertible into or exercisable or exchangeable for any Common Stock, 

 

whether any transaction described in clause (i)
or (ii) above is to be settled by delivery of Common Stock, other securities, in cash or otherwise. Moreover, if:

 

		(1)	during the last 17 days of the Lock-Up Period, the Company issues an earnings release or material
news or a material event relating to the Company occurs, or 

 

		(2)	prior to the expiration of the Lock-Up Period, the Company announces that it will release earnings
results during the 16-day period beginning on the last day of the Lock-Up Period,

 

    	 

    	 

    

 

the Lock-Up Period shall be extended and the
restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the date
of issuance of the earnings release or the occurrence of the material news or material event, as the case may be, unless MDB waives,
in writing, such extension.

 

Notwithstanding the provisions set forth in
the immediately preceding paragraph, the undersigned may, without the prior written consent of the Company, (1) transfer any Common
Stock or any securities convertible into or exchangeable or exercisable for Common Stock as a bona fide gift or gifts, or by will
or intestacy, to any member of the immediate family (as defined below) of the undersigned or to a trust the beneficiaries of which
are exclusively the undersigned or members of the undersigned’s immediate family or to a charity or educational institution;
provided, however, that it shall be a condition to the transfer that (A) the transferee executes and delivers to the Company
not later than one business day prior to such transfer, a written agreement, in substantially the form of this agreement and otherwise
satisfactory in form and substance to the Company, and (B) if the undersigned is required to file a report under Section 16(a)
of the Securities Exchange Act of 1934, as amended, reporting a reduction in beneficial ownership of Common Stock or any securities
convertible into or exercisable or exchangeable for Common Stock by the undersigned during the Lock-Up Period (as the same may
be extended as described above), the undersigned shall include a statement in such report to the effect that such transfer or distribution
is not a transfer for value and that such transfer is being made as a gift or by will or intestacy, as the case may be or (2) exercise
or convert currently outstanding warrants, options and convertible debentures, as applicable, and exercise options under an acceptable
stock option plan, so long as the undersigned agrees that the shares of Common Stock received from any such exercise or conversion
will be subject to this agreement. For purposes of this paragraph, “immediate family” shall mean a spouse, child, grandchild
or other lineal descendant (including by adoption), father, mother, brother or sister of the undersigned.

 

The undersigned further
agrees that (i) it will not, during the Lock-Up Period (as the same may be extended as described above), make any demand for
or exercise any right with respect to the registration under the Securities Act of 1933, as amended (the “1933 Act”),
of any Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, and (ii) the Company
may, with respect to any Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock owned
or held (of record or beneficially) by the undersigned, cause the transfer agent or other registrar to enter stop transfer instructions
and implement stop transfer procedures with respect to such securities during the Lock-Up Period (as the same may be extended as
described above).

 

In addition, the undersigned
hereby waives any and all notice requirements and rights with respect to the registration of any securities pursuant to any agreement,
instrument, understanding or otherwise, including any registration rights agreement or similar agreement, to which the undersigned
is a party or under which the undersigned is entitled to any right or benefit and any tag-along rights or other similar rights
to have any securities (debt or equity) included in the offering contemplated by the Underwriting Agreement or sold in connection
with the sale of Common Stock pursuant to the Underwriting Agreement, provided that such waiver shall apply only to the public
offering of Common Stock pursuant to the Underwriting Agreement and each registration statement filed under the 1933 Act in connection
therewith.

 

The undersigned hereby
represents and warrants that the undersigned has full power and authority to enter into this agreement and that this agreement
has been duly executed and delivered by the undersigned and is a valid and binding agreement of the undersigned. This agreement
and all authority herein conferred are irrevocable and shall survive the death or incapacity of the undersigned and shall be binding
upon the heirs, personal representatives, successors and assigns of the undersigned.

 

[Signature Page Immediately
Follows]

 

    	2

    	 

    

 

IN WITNESS WHEREOF, the
undersigned has executed and delivered this agreement as of the date first set forth above.

 

	 	Yours very truly,
	 	 
	 	MDB CAPITAL GROUP LLC
	 	 
	 	By:	 
	 	 	 
	 	Print Name:	 
	 	 	 
	 	Its:	 

 

Signature Page — Letter to

MDB Capital Group LLC and ClearSign Combustion CorporationDated as of March ____, 2012

 

MDB Capital Group LLC

401 Wilshire Boulevard

Santa Monica, California 90401

 

ClearSign Combustion Corporation

12870 Interurban Avenue South

Seattle, Washington 98168

 

Ladies and Gentlemen:

 

This agreement is being
delivered to you in connection with the proposed Underwriting Agreement (the “Underwriting Agreement”) between
ClearSign Combustion Corporation, a Washington corporation (the “Company”), and MDB Capital Group LLC (“MDB”)
relating to a proposed underwritten public offering of shares (the “Shares”) of the Company’s Common Stock
(the “Common Stock”).

 

In order to induce
MDB and the Company to enter into the Underwriting Agreement, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the undersigned agrees that, during the period beginning on and including the
date of the Underwriting Agreement through and including the date that is 180 days after the date of the Underwriting
Agreement (the “Lock-Up Period”), the undersigned, or any affiliated party of the undersigned, will not,
without the prior written consent of the Company, directly or indirectly offer or sell in any public market on which the
Common Stock of the Company is actively traded any of the Shares. This is a limited lock-up, and specifically does not
prohibit the undersigned from distributing the Shares as a dividend or otherwise offering or selling the Shares in a private
“off market” transaction. To the extent that it is able, but it is not a requirement, the undersigned, in
connection with a distribution or private “off market” transaction effect a transfer of the Shares in such a way
as to continue the Lock Up Period while in the hands of the transferee of the undersigned.

 

The undersigned hereby
represents and warrants that the undersigned has full power and authority to enter into this agreement and that this agreement
has been duly executed and delivered by the undersigned and is a valid and binding agreement of the undersigned. This agreement
and all authority herein conferred are irrevocable and shall survive the death or incapacity of the undersigned and shall be binding
upon the heirs, personal representatives, successors and assigns of the undersigned.

 

[Signature Page Immediately
Follows]

 

    	 

    	 

    

 

IN WITNESS WHEREOF, the
undersigned has executed and delivered this agreement as of the date first set forth above.

 

	 	Yours very truly,
	 	 
	 	INTEGRATED SURGICAL SYSTEMS, INC.
	 	 
	 	By:	 
	 	 	 
	 	Print Name:	 
	 	 	 
	 	Its:	 

 

Signature Page — Letter to

MDB Capital Group LLC and ClearSign Combustion Corporation

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