The exclamation mark is extraneous and creates confusing a visual indicator as to whether a link is to the hosting instance of the community rather than a link to the federated copy on whatever instance you're on. It works one way in some circumstances and the opposite way in others. And it won't work at all for people who are on an instance that hasn't federated with that community. It has in fact been depreciated by the main devs of Lemmy but that's only documented in comments to github issues.