He said it first in an op-ed in the New York Times in 1986:
"Everyone detected with AIDS should be tattooed in the upper forearm to prevent common needle users, and on the buttocks."
He repeated the idea in 2005:
"Someone, 20 years ago, suggested a discreet tattoo the site of which would alert the prospective partner to the danger of proceeding as had been planned. But the author of the idea was treated as though he had been schooled in Buchenwald, and the idea was not widely considered, but maybe it is up now for reconsideration."