Actually, about 2 minutes after my friend sent that link, I thought to myself "why not just use dice if you're concerned about it?".
If you get a little of that silly putty type of stuff they put under stuff on boats to keep them in place, you can stick a die to the mirror or wall.
If you're really dumb and can't tell the difference between a blade used 6X and 1X you can use a pair. If you have a 5 razor rotation, think of the money you'd save.
Maybe I'll package a couple dice and a glob of putty up with instructions and sell it for $6 as "Count Blade's Shave Tracking System and Portable Craps Game"
Two uses in one and a bargain at half the price!
A while back, a noob asked what the numbers on a DE blade were for. Someone else posted an elaborate scheme to use them to track not only how many uses the blade had, but to make sure he turned it over the prescribed number of times so as not to wear the edges unevenly! It almost sounded believable. I think it took a while before the OP realized his leg was being pulled. Hilarious.
Wait, you are supposed to flip the blade for even wear??? Why didn't any one tell me this?