You can get profile pictures off Google images and click on "line art" ... silhouettes I think comes up with a lot of choices.
Depends on what "style" you are going to do and what "type" of rally. If it is a charity event, then I would go with a simple theme of various outlines. If it is a "rally" you might want to decide if you want a "racier" type quilt.
Remember, what/who they act like at a rally isn't what they may be in "real" life so they still will like "pretty & fancy" quilts, they don't have to be hardcore.
Hope this helps :)