I don't know how widespread this is, but when I went to get surgery on my foot (NHS in the UK) they literally drew an arrow on my leg with a marker pen to avoid operating on the wrong foot haha.
One of the first steps the day of was the surgeon coming in, talking to me, and initialing the shoulder he was to operate on.
Every new person I met along the way asked me what shoulder it was, and then wanted to see the initials before continuing.