As a physician I am aware of all manner of horror stories. When I had my ACL repaired several years ago the surgeon gave me a magic marker and told me to mark the knee he was supposed to operate on, just for certainty sake. I drew a line across my thigh above the knee, then an arrow pointing down toward the knee saying "cut here". I then drew another arrow pointing up my thigh above the line saying "don't cut here". My surgeon said the anesthesiologist and OR nurses busted a gut when they uncovered me to prep my knee after I was asleep.