In some of the country pubs that I go to in my area, there's a popular pastime known as “nookie-watch.”
Being a few miles out of the city, they're often used for anonymous dallying.
A couple sits quietly in the corner.
If they lean back without eye-contact or conversation, they're obviously married.
If they lean in, smile a lot, being a tad over-attentive, then they're on a date.
If he has a clean shirt, then it's a first date.
If they appear a little over-excited and constantly look at their phones, then they are with someone else's husband/wife.