This would have been a good thing to have on my last flight - I was napping but had to keep waking myself up to keep an eye out for the breakfast service. I guess I could have just written a little sign for myself, but that would be wierd. Definitely would make air travel just a little more enjoyable!

would have appreciated this a few days ago when the stewardess yelled "wakey wakey" while shoving a stale croissant in my face

This could've saved many unnecessarily unpleasant flights - I like it.

I like this idea. An added benefit would be the "signal" you send to the person beside you who will not stop talking when you want to read, sleep, or just sit in silence. Few people have the guts to say outright that they don't want to be disturbed.

Most airlines already provide this service (at least in business class).