I think it would be helpful for everyone's understanding if a note was posted on the bottom of locked threads. I don't think it's very realisitic to expect people to read the whole of a locked thread, re-read the terms and conditions and guidelines and re-interpret and then apply them. A note would serve to remind people of the reasons.
I dont really think it is unrealistic though. People who post here know the rules - new or veteran posters. They are clearly stated and pinned in the first board on the forum - and as with any forum, they should have been read before posting.
Most topics that I see that are locked, it's pretty obvious the reason - venting, sensational news stories, topic done to death, politics/religion, etc. I have seen maybe 1 or 2 topics that were locked that I wasnt sure why, and my only thought then was "Hmm, wonder why that was locked? Must have been something going on there." The truth is, if you have time to peruse the forum, you have time to review the rules to figure out why a thread was locked. The moderaters have chosen to spend time moderating, rather than explaining. Fair enough.
Yes, sometimes it makes me nervous to see threads locked down (especially since there have been so many lately). But I know the rules and I stay within them, and typically I can identify the rule being broken from the first post. And if I'm not sure, I go review the rules. I'd imagine that a gagging would come with an explanation, or at least a few warnings beforehand, so that the poster would know what they did that was outside the rules. Other than that, I dont see why a poster would really need a mod to explain things. Yes, it would be nice, but certainly not necessary.