I recently ran into a few posts where a commissioner tagged themselves on the posts. I removed the tag while adding other tags (where it didn't have many to begin with) as I'm quite sure I read that the commissioner shouldn't be tagged on posts. I got messaged by said commissioner asking me to stop removing their tag, and I was going to reply with information about not tagging the commissioner of a piece. But I'll be damned if I can't actually find any rule, guideline, or even an admin statement about it. I found this forum thread from 4 years ago saying it's not preferred to tag the commissioner, although the last two posts (necro'd 9 months ago) suggest that this has been tightened. And indeed, looking at the edit history of the person who necro'd that thread, all the commissioner tags they added were removed by admins. But I still can't find any official guideline or statement.
So, am I remembering correctly that a commissioner for a piece shouldn't be tagged? Am I overlooking where it's mentioned, and/or should it be added to the wiki or help pages somewhere?