For skuas you only need "reasonably large"Well, you could follow the FAA's rules to the T and put 12" letters on your Phantom!
It'll look pretty messy.
I printed mine on Avery type labels and put the N-Number and my phone number on the sUAs and my transmitter. Total cost, less than 50 cents.
But then you have to factor in the cost of the paper, the ink, the wear-and-tear on your printer...
Just kidding... That's a great idea, but for some reason I've never had any luck using Avery labels, they never seem to stick for me, not even on paper...