I have a fond memory of being at the top of Elm Row in Edinburgh when I saw a little squirt throw some item a bus. The driver did not flinch (it was soft and did not damage the window) and simply drove on.
Little squirt chortled with his friends.
Less than a minute later a Police car tears around the corner (we were almost on top of Gayfield Police Station), and out leaps a female officer who grabs little squirt without paying any attention to his friends. Clearly there was CCTV on the bus, and a direct link to the Po-Po.
Either little squirt was splashed by cars driving through puddles, or he made at a little squirt himself.
In contrast, Stagecoach buses in Caithness do not appear to have such equippment as local Police still are seeking the Wick High School pupils who smashed the windows of a moving bus last week.