There was once this creep, back in Malaysia, who was wearing dark glasses at night. We checked and found out that those glasses were night vision ones. He was spying in the girls. He belonged to a certain country as well.

And they wear dark glasses so as to hide what they're looking at, to observe people without their knowledge. Creepy if used for voyeurism, etc.

But on the other hand, some do it to observe their staff, to ensure that the naughty ones are working and not skivving - but this one, usually, during the day time when it's sunny and not so obviously out of place.

*****************************************
Don't want no drama,
No, no drama, no, no, no, no drama