What counts as an official on-screen sighting?

We notice every time a character on screen chooses to throw away, drop, or leave behind something artificial, with no plan to return for it or put it in a bin. This might be a cigarette flicked away, a fast food bag tossed from a car, a phone smashed on the pavement, or a coffee cup left on a bench. If something is left behind and becomes part of the scenery, we include it.