A google search for "All of these men have it" "Stay away from dance halls" mainly got web 2.0 user generated content websites such as reddit and pinterest. I came across a thesis, but it gave a different year, saying that it was 1942.
By contrast, doing a search on the image gave a New Hampshire government website, with the following poster, by Montgomery Melbourne in 1943:
Millions of troops are on the move…
Is YOUR trip necessary?
OFFICE OF DEFENSE TRANSPORTATION
Another page with this poster is the University of North Texas Digital Library which specifies that the Office of Defense Transportation was US, not British (it was an executive agency).
Montgomery Melbourne's name can be seen in the original in the bottom left hand corner of the picture - the same writing can be seen in the "Syphilis" version, although not legible.
In summary, there exists a poster with the same image, but a different message, by the government of another country, from a different year. It's possible that an image was re-used for the syphilis warning, but there's no reason to believe that's the case.
I have to admit it's a fairly good hoax: it talks about a disease which is not commonly talked about nowadays, and a form of socialising that isn't popular nowadays.