For the US
military folks, the
US Uniform Code of Military Justice specifically
prohibits
Public Display of Affection, especially if it is between
two uniformed individuals. I remember getting chewed out by an
Ensign because I had my hand on my girlfriend's hand on a table. Guess he was
jealous, she was one of the few women who looked great in uniform.
There are always exceptions, though. The most notable one is when a ship returns from a deployment. There is more hugging, kissing and groping going on than a Roman orgy, but nobody really minds.