They must be easily and quickly understood by an average person. Time your event with an anniversary, this will enhance your demonstration. Provide opportunities for pictures. Newspapers don't always have space for a detailed article, but one photograph could help a lot. This will also attract TV, a visual medium.
Costumes often make dramatic statements.
If you have speakers, make sure to have an adequate sound system. If they cannot be heard and understood, you will loose your audience, especially the media. If you start with horn honking, arrange to have it quieted down and regain the everyone's attention first, then begin. Have printed materials available for both the public and the media about your issue. Make sure the material lists contact names and phone numbers.