Every so often, a new question is asked by someone inquiring why their rep didn't go up, even though it should. These are (nearly) always closed as a duplicate of the FAQ entry, "How does 'Reputation' work?". Either users aren't reading the FAQ, or they do, but don't read it all because of how massive it is. I think we should notify users the first time they hit the rep cap. Maybe a simple Stack Exchange™ MultiCollider SuperDropdown™ notification?
As discussed in the comments, the wording of the Mortarboard badge can also be confusing to new users (emphasis mine):
Earned at least 200 reputation in a single day.
While it is possible to earn more than 200 reputation in a day, the wording can be misleading and make someone unaware of the rep cap think they can get 200 reputation from votes. The wording doesn't have any mention of the rep cap.