Not flash but does the 310 still support the message command? If so "message (whatever you want here)" will display the provided message on a black screen?
I know that I can cause the TSR-310 screen to flash (as an ID'ing tool) with the AppleTV Control reserved Join extender, But does anyone know if there's a way to flash the screen without this extender? (I don't have it in the program I'm working with...)