Love that sign! Seen it 50 sixty times over the last 30 years or so, I never say any reference to homosexuals, mostly get out of the UN, and other stuff. I think the author might have made that anti-homosexual up just to make him fit the wacko-prototype....
I lived within about 10 miles of the Uncle Sam sign during the late 70's up through the mid-80's. I've driven past it 100's of times. I don't recall any comments aimed at homosexuals, but I wouldn't be surprised if he put some up. I always looked forward to whatever he had to say...it was usually good for a chuckle.
Here's one from the archives about homosexuals:
AIDS TURNS FRUITS INTO VEGETABLES.