Rainbow Magic Marking. At our old league, every shooter had his own color pattern he drew across the heads in stripes. Since we were shooting low-pressure target loads, my dad used a hacksaw to put a groove in his case straight across the diagonal. I was the first in the league to try Top Brass and Starline cases just because nobody else had those headstamps at the time. If you have a use for 50,000 pieces or more in one purchase, Starline will put your personal headstamp on them. Winchester offered that service for a brief time in the 80's on orders of 2,000 or more. I wish I'd had the money at the time just for the novelty of it.
One thing I've done to keep track of how many loads have gone through a case is to use an automatic center punch to mark the head. You could do that for identification, too, but it isn't very clear from a distance.