This will make knowing who's banned in general easier, and will teach newer users what you could get banned for as well. This probably won't be updated every time somebody is banned, so having this in the profile page wouldn't hurt. Possibly written in bold red under the 'type' section (type: banned user, for example).
If that thread isn't updated all the time, then a user's profile is not gonna get updated all the time either. Most times it's pretty clear why they were banned.
