Need to have users "sign" a waiver when RSVP'ing to an event


I realize this is probably not an Event+ issue, but I was hoping someone might be able to offer some advice on how to do this or point me in the correct direction.

We are a mountain biking club and someone could get hurt so the boss wants to add a waiver/disclaimer when some is RSVP’ing to an event.

Any suggestions, advice, or links to helpful sites would be appreciated.