Pregame dunk - mechanics

So, I experienced a pre-game dunk for the first time last night (they usually know better at the varsity level). I didn’t signal the T, I told the guilty party to go tell his coach why he lost his box, unfortunately he didn’t speak any English…
So I informed the coach during pre-game & he already knew the deal. He attempted to argue that the indirect didn’t forfeit his box, but he sat the whole game anyway... nice try coach
My partners suggested that after intros we take our positions then I should signal the T as the players took the floor, so everyone knows why. I didn’t like it, so I told the PA announcer to make the announcement after the National Anthem.

How do you guys handle that situation? Do you signal the T right there on the spot with a whistle or after intros or not at all? Do you tell the coach right then & there or do you wait until pre-game with coaches?


Thanks much!