There have been a lot of people asking about whether sign-up posts in clubs count for the Post-A-Thorn 2.0 challenge. The answer is so they, permitted that a topic is answered at the same time. If you just fill out a sign-up form then the post does not count as there is no real contribution to the club. However, if a topic is answered within the post (either as a part of the sign-up form or separately), the post can be counted for the challenge.
Hope this clears up some issues and make sure to make contact if you have more questions! ^^