In English literature, the direct speech of imaginary characters is typically marked with quotation marks. An imaginary character says, “Do not throw trash in the tray.” Perhaps your mother?
Literary style seems to have become a deeper part of consciousness than verbal grammar. An ATM deposit envelope provides the setting. Written on it is a bare noun phrase, although it could be an imperative statement if the ATM had needs: DEPOSIT ENVELOPE FOR ATM. Then a stern, laconic voice says, “NO COINS”.
The whole world is not naturally made of narrative. Historical contingencies of intellectual life and technology have constructed it that way.