In Nazi-occupied Europe during the Second World War, the resistance would freak the fascists out by secretly painting the "V" symbol everywhere: on roads, on walls, carved into stone etc. If a Nazi entered a bar, someone would tap under the table with V in morse code. The Nazis had no idea who was doing it and they couldn't arrest the whole bar.
"...the (Nazi) occupier, by seeing this sign, always the same, infinitely repeated, (would) understand that he is surrounded, encircled by an immense crowd of citizens eagerly awaiting his first moment of weakness, watching for his first failure."
https://en.wikipedia.org/wiki/V_sign#Second_World_War:_V_for_Victory_campaign
