First, the red circle w/ diagonal bar I’m referring to: “No Symbol”.
I think this symbol was developed for international traffic signage during the 1960s, but Wiki gives no real history in the entry.
Anyway, advertising and art have, while not co-opting the symbol completely, certainly embraced it - and there are plenty of such non regulatory uses in icons, ads, avatars, visual signatures and so on.
The question is: when did the first ad-man/graphic artist (or both) apply the No symbol to regulatory activities (such that it made a mark on human culture - a high-school kid doodling in his notebook in 1974 and nothing coming of it obviously wouldn’t count, while say a small chain of hot-dog places that had a “No Burgers” symbol in 1976 might count). The earliest I can think of is the GhostBusters logo from 1984 which the Wiki entry mentions:
This may fall into 2 “firsts”:
Pure “art graphics” as you may find in signatures, T-shirst, Avatars and so on (e.g. No Trolls, No BullS***, No “FAT” whatevers)
Actual warnings without legal force, but helpful for everyday life - No Bleach, Do Not Disturb, Do Not Stack etc.