If I block someone on messenger..

[Worththewait2019]

What does it look like to them? Does it show I've blocked them?

Are you talking of Facebook messenger?

If so... When someone is blocked, you don't appear to them. So you become invisible, so to speak.

But if they're in your messenger already they'll know you've blocked them because they won't be able to reply to the last message.

If you block them completely they can't see you at all.
If you just block them from messaging you it says something like "you are unable to send messages to " and they can Dee your profile completely and all the previous messages but they can't contact you.