(points the group to
www.wheresgeorge.com)
It's legal to mark money--just as long as you don't make it unfit for reissue.
Although given the volume of money in our country today and the relatively small number of FIRST teams, I highly doubt that any team would be able to find another team's bills outside of FIRST-heavy events...namely regionals and the championship. But then at the championship, any place much away from the Georgia Dome would have a significantly lower probability of sending out FIRST money, since it'd get heavier civilian (for lack of a better term) traffic.
But that's just my speculation...YMMV.