Signaling is of interest only because it is used in advancing the joint activities people are engaged in. Take this exchange from an interview by a British academic of a prospective student (3.1.174):

Arthur: u:h what modern poets have you been reading -

Beth: well I'm. I like Robert Graves very much -

When Arthur says “u:h what modern poets have you been reading -” he doesn't want Beth merely to understand what he means – that he wants to know what modern poets she has been reading. He wants her to take up his question, to answer it, to tell him what modern poets she has been reading. She could refuse even though she has understood. To mean something, you don't have to achieve uptake, and to understand something, you don't have to take it up. Still, Beth's uptake is needed if she and Arthur are to achieve what Arthur has publicly set out for them to do at this point in their interview.

Arthur and Beth's exchange is used to carry out a joint project. The joint project begins with Arthur projecting a. joint task for Beth and him to carry out – she is to tell him what modern poets she has been reading. It continues with Beth agreeing to that project, and it becomes complete, though slightly altered, with her answer. A joint project is a joint action projected by one of its participants and taken up by the others.