Somewhat related: On a KE flight earlier this year in Y, I slept through a meal service and awoke to find a sticker on the seatback in front of me informing me that I could have my meal at any time upon request. Still groggy, I peeled off the sticker to have a closer look. Literally within seconds, an FA noticed this and came by. A couple minutes later I was eating my meal, quite impressed at the attentiveness of the service.

I must get one of those to put on my flight bag :D

Maybe cut eye holes a la Zorro. :D

I love that we're talking about "Do Not Disturb" signs and not the mealy-mouthed and indirect "Privacy Please" signs that all hotels use these days.

IIRC, some of the amenity kits have those little signs tucked inside of the bags.

Can't find it now but there is also a website that sells blankets that has signs on it saying something like "eyes no open - mouth no eat"

I have a collection of "Do not disturb" stickers from emirates flights. You stick it on the seatback and usually the FA will leave you alone. However, on seats which recline a lot (i.e. J class) sometimes you can't see the sticket and I don't know where to put it. :(

Cheers,

You could get a canvas hat with a huge button that says "Jesus Saves" or "Lose Weight Now - Ask me How" and pull it down over your eyelids.

KE has it too

"Do Not Disturb" Sign
 

http://estore.thewhimbles.com/products.asp?dept_id=167 - scroll down to third item

Years ago you used to get the Do Not Disturb / Wake For Meals stickers on UA too. Problem was I was never really sure where to put them (if you put them on the back of the seat in front of you and the seat then reclined they wouldn't be seen). I have a "no service" policy on all my east coast departure transatlantic red eyes, and as others have said a word with the FA in the galley during boarding ensures that no-one says anything to you at all until you need to put your seat up for landing.

Put it on your forehead...

Not a bad idea. Especially for many airlines that have created closet like suites in F where such tags can easily be treated like the hotel room door. ;)

IIRC the EK A345 suites have a button you can press to illuminate a DND light. Not sure if the other enclosed suites (eg SQ) also have this.

If you're in first class just tell them. It's small enough for them to remember. Just ask it nicely and say that while you appreciate the server, you really don't want to be disturbed. Tell the person you will let them know if you need something.