As above, I'm not sure you can actually do anything without blocking out the UV as that's what's fading the sign. You need something that will that will cut out the UV. I'll have a little think, I'm not sure whether I've ever dealt with anything similar historic building wise, but I'll have a look.
Plant a tree, Or have a larger overhang over the garage roof to keep the sign in the shade. Take a painting course so you can repaint the sign each year. A few options for you, I'm sure there are more.
already planted trees in the little bit of waist land at the end of the small field ,, oak trees apple trees pear trees cherry trees and loads of differant bushes as well just need them all to do well in growing,