I have applied vinyl lettering/graphics to more awnings than I care to remember, including on with 22" letters going 30'. In fact, the customer refused to get a permit and got busted by the City. Luckily they liked it and approved after the fact when she paid for the permit and fine. It does have to be clean and dry, after soap and water use alcohol. Don't try it if the temperature outside is under about 60, 70+ is better. When peeling the transfer tape, go slow when you get to a sharp corner on a letter.
Sammamish, WA
Epilog Legend 24TT 45W, had a sign business for 17 years, now just doing laser work on the side.
"One only needs two tools in life: WD-40 to make things go, and duct tape to make them stop." G. Weilacher
"The handyman's secret weapon - Duct Tape" R. Green