Friendly reminder

If they have to say it's "friendly"... it's not. It's a reminder with a strong hint of consequences if it's not followed.

Sometimes management sends something like this to a whole group when only one person is doing something management doesn't want, instead of just talking to that one person. They're hoping the one person will take a hint, realize it's him/her, and change. It often doesn't work, but management does this because they just don't feel like confronting the problem.