I don't know if the thicker Sharpies fade - we used them at the lab all the time and I never saw fading. They just aren't easy to write small. They do make a super version that doesn't come off with alcohol or anything else, too.
But, that said, I'd check the scrapbooking section of a craft store (like Michaels or ACMoore) or the drafting supplies section of a craft store. Read packaging - there might be something there that won't fade.

And I'm all for IDing subjects, dates, and locations on prints. I have a huge pile of negatives and prints that aren't labeled and the people who could ID them have mostly passed away. Reminds me I should be better at labeling prints.