@helen ann I do not believe your idea was "silly".
Having read through all 14 pages I think some people may have read between the lines on the OP for something that wasn't actually written.
As long as the goal/solution does not require the labeling/shaming/banning of any individual for a past deed they may have already atoned for I don't see how this isn't seen as a good idea as it would have very minimal impact on vendors and attendees. Bottom line, is that whatever is implemented or not, should have no effect on vendors/attendees to make transactions.
Based on my reading, here is where I think the idea currently stands - and feel free to correct me if I am wrong or misunderstanding - and what I have seen that would be considered viable and agreeable solutions.
Banning/Labeling (or non-labeling)/Shaming -
wrong, and should NOT be done. So the idea of the sticker/poster for individuals/booths should not be done as to not single any vendor(s) out and tread on their legal rights.
"Safe Zone" -
good. In my opinion, I think there should be two "zones" at the events, one near the entrance and one as close to center as possible, just for the event that parent/child are separated, and who wouldn't also agree this would be a good idea for spouses/friends as well? (When my wife and I are accidentally separated w/ a dead phone(s) at Disney - Magic Kingdom, the People Mover is our predetermined meet up location). If these "zones" become staples they could become easy land marks/navigational items for getting around the shows.
Background Checks -
mixed. I like the thought of background checks for anyone who
wants to volunteer to work the "safe zone", but should
not be required of any vendor or attendee of a show. I also agree that these could/should be people trained for these kind of programs (LE, FD, or other professional) and not just any attendee. If it is done on a volunteer basis, maybe these people work in shifts and get in to the show free? (Comment on the cost, from my understanding there are different "levels" of background check here in Central FL where I teach, we are required to have a Level 2 background check which requires fingerprints and runs $125-150 but Level 1 checks are $30-40)