[R. Scott]

When my late wife went in for knee surgery I wrote on one with a magic marker, “not here”.

[Pollster1]

I did that too, and the surgeon wrote a funny note in response. Afterward, he mentioned that notes are a good idea (totally unnecessary at Johns Hopkins, in his opinion, but useful in many other places).

[Lonesome in Massachussets]

Bad move. If you mark both knees (especially in the same color) you're inviting trouble. When my daughter had orthoscopic surgery on her knee, the doctor handed her a magic marker to mark the knee being operated on. If you are going to mark both knees mark one in one color (operate here) and one in a contrasting color (not this one) And don't use any of the same words in either message, e.g., not "don't operate here" vs "operate here". And always have all the patients do it the same way under your instructions.

[MisterArtery]

I hope you wrote on the correct one!