Typing a community name with an exclamation mark in front of it generates different links for different instances in the Fediverse, so that the UI doesn’t change for people on other instances. ;)
Just an example:
These are both the same community, on kbin. You are a Lemmy.world user, so clicking the first link will redirect you to the magazine on kbin, but open it in the Lemmy.World UI and you can vote, comment, post and everything else. Someone registered on Lemmy.ml can click that link and get the magazine with the Lemmy.ml UI instead.
Clicking on the second link however will always open the kbin UI no matter what your home instance is, and unless you’re a kbin user already, you can’t vote, comment or post.
SaintWacko@midwest.social 6 months ago
In some clients, that will turn into a link to the community. As such, it’s sorta become a way to say “the following word is the name of a community”