Okay, so I was Googling for removing paint off tires and came across a thread which Mike replied to:
http://www.autogeekonline.net/forum/ask-expert-featuring-mike-phillips/20882-spray-paint-tires.html
So I went to Lowe's on the way home and picked up a bottle of Motsenbocker's Lift Off Spray Paint Graffiti for about eight bux and tested it on some spots. I sprayed it on and then waited about a minute. At first it didn't seem to do anything. After a few attempts, it magically started working. After soaking for a bit, I rubbed my thumb on the paint and it started smearing. Anyway, here are some before and after shots. I stuck some tape as markers.
Just a word of caution; don't use it on leather sofa. I should have tested it first in an inconspicuous spot. Oh well, live and learn.