Ketchup doesn't look too much like real blood; so if you don't mind stains, try honey mixed with red food coloring. I would really rather use that area for the crosswalk beat-downs.
I would prefer using ketchup packets visibly, as if they were some form of "deadly weapon", or even yell out "You made me bleed ketchup!" when you're covered in it.
A good one is to get a long roll of Saran wrap or long, thin strings and tie them between trees or signs. When a car goes through they can hear the popping and ripping and such.