These "Free Babylon 5" posters I've seen here (great artwork!) won't do the job, I'm afraid, because unless average audiences know what it's about, why would they care to "free" something they don't know?
The idea wasn't to attract new people, but to get the attention of existing fans for them to help with the actual campaign. Obviously people who don't already know the show will know or care what Psi Corps is, nor get the Peanuts reference. Honestly I thought that was self evident.