These are my steps on how to participate in signature campaign:
1. Look for a project that you believe in and has great potentials to be one of the top crypto: you can refer to the bounty list here: https://bitcointalk.org/index.php?board=238.0
2. Read carefully the instructions on how to join the signature campaign. Some project requires Member rank and up to be able to join the signature campaign but some accepts Jr. Member or even Newbies.
3. Fill up the form to register for the signature campaign. You need to post proof of authentication or something in the thread first because it will be ask in the registration form what application number you are applying for.
4. Next is to wear the signature. Be sure to use what specific signature you will use depending on your rank. There is additional stake if you wear Avatar but it is allowed only for Full Member rank and up (if I remember it correctly).
5. And last is to post on threads, minimum of 75 characters and atleast 10 posts per week (depending on the rules of the signature campaign so it is very important to read it again and again if things are not clear to you)

Hope it helps! Cheers!