The sign is probably some kind of a "black humor".
But - generally - it`s not ok to be gay in Russia. No one will know for sure unless you tell, but my advice would be to avoid provocative cloth, haircuts, conduct... Don`t smile too much to strangers (I`m not kidding). On the other hand, I see lots of lesbian girls in St Petersburg, sometimes even male couples - mostly in the city center. So the truth would be to smother the personal life questions like..
...but then they would wonder how come a guy in his 30's is still single.
1. Busy man (high achiever with not much free time). 2. Broke up recently, still suffer, no impetus to find a new one...
Stay safe.