Sentence:  Please find the larger group <WSD>sign-on</WSD> letter attached for comments/feedback. Send any comments to Daniel Dawes at: @ by Tuesday, April 28. Remember -- this is just a draft. After this letter has been vetted by you all, we will send out a final copy right after <WSD>sign-ons</WSD>. 
Meaning of the word marked with <WSD> tags:  (more generally) An instance of signing on to something.