Obviously the sign is ironic. I like this sign a lot. It makes fun of religious fundamentalist homophobics while educating people on the life of one of the greatest minds of the 20th century, Alan Turing.I still can't believe there are people who care that much about what other people do privately, and this sign takes it to a stupid level. Sadly, I probably interact with people that think like this regularly.
Is the sign intended to be ironic?
Turing did in fact help a lot to shorten WW2 by cracking the nazi encryption. He was also a very important pioneer of not just theoretical computer science but also of artificial intelligence and machine learning, as well as the biological field of morphogenesis. And he was tragically driven to suicide (at the age of 41) because being gay was illegal in the UK at that time: he was convicted of having commited acts of homosexuality, admitted this "crime" and got convicted to chemical castration (a hormonal treatment which a.o. gave him breasts).
All in all this is a very sad absurd-but-true story: a war hero and great intellect (comparable only to Einstein and Gödel) essentially got murdered in 1952 by a Victorian anti-gay law from 1885 (decriminalization only happened in 1967 in England).