Do you mean "distressing" as in making it look older? When I was playing with lettering on my Austin, I simply used 400 grit sandpaper and carefully sanded the lettering after I painted it on. I cut the paper into strips that were close to the size of the letters, and then just gradually sanded it at various spots to get it to look worn through. Must have worked, because I kept getting guys telling me they'd seen it run back in the 60's. I finally repainted the car, and did new lettering, as I actually got tired of arguing with guys that wouldn't believe I had just built the car that year.
local brush-master in town told me that just before the paint dries, he uses thinner, to wipe the fresh paint to make it look dis-stressed. any video's out there showing this?
my guy uses sign paint and thins it with a little alcohol so the brush strokes look uneven. then I give it a light sanding with 400
my advise would be to get your local "brush master" (or a real signpainter) to do it for you, ask if you can watch, practice on a scrap piece of metal, it won't be as easy as he makes it look and cannot be mastered in a couple of days.