Something we learned the hard way at Bayou 2010: Don't put off numbers if they have to go on the bumpers...if you're having to use paint outside, the result will look like crap.
JVN's silver Sharpie tip was a revelation this year, though that still took us a couple of hours in our shop with a small group of people tracing and going back over the numbers a few times. (I think we put at least three or four coats on
our robot's bumpers, which we did with a rather thick stroke--we bought six markers and had usable ones afterward.)
I wouldn't want to do anything resembling that level of effort in the pits ever again.