Or we could just simply say no solicitations, and kick-ban violators for three days.
I don't think banning someone for 3 days for posting about a fan-film fundraiser is appropriate. When people make posts like that, they are just trying to help filmmakers out. People shouldn't be punished for good intentions. The best thing to do is to close the thread whenever this happens, and for the Moderator to message the person who posted the thread about why it was closed, so it doesn't happen again.