You can just type in your activation code on a new device. If there are unassigned licenses left, everything will work as usual. In case there are no licenses left, the activation will fail but an automated email will be sent to email address that was used during the purchase. This mail will contain a list of web links that, when opened, will ‘clear’ a license that is assigned to a particular device.
Devices are identified by ID and license activation timestamp. You can find out device ID if you start Signature Capture application, press Menu and then About.
A small note: these ID’s are modified by Android system when factory reset is performed.