In Business Class, they usually ask if I would like to be woken for arrival service when they talk to me for initial meal choice. Often they also ask which choice I would like for arrival meal.
Alternatively, the Polaris amenity kit now contains a sticker for "Do not disturb", IIRC.
As for economy, I believe the most recognized "signal" that you would like to be included in the service is to lower your seat-back tray. I know it works very well on short-haul.