Find a decal on a machine, that is in EXCELLENT condition, or find one on the net. Either way, take a photograph of it (or copy and paste off the net), tweak it in Photoshop, or similar, and print it off in full colour, maybe a few copies, on real glossy paper.
Buy some clear spray paint lacquer. Repeatedly spray the face of the photo's with the lacquer, over a couple of days, so they are real glossy.
Soak the photo's in warm water, with a little soap for a little while, and the paper will eventually peel off the back, leaving just your lacquer, and the coloured prints.
Buy some white enamel spray paint. Paint the REAR of the now almost translucent pictures with a few coats of white, to give the background some solid detail, let dry.
Using scissors, or a knife, cut out what you want, and discard the rest.
Using your clear lacquer, spray the REAR of your photo, and place it on the machine, smoothing it out VERY gently. Spray a bit more all over once in place, to feather the photo edges to the machine.
Did this a few years ago using a picture in a magazine, and placing it on my tank. Yes, it DID fade, but it was heaps cool. This was a method of detailing cars and bikes before Air brushing came into vogue with good artists for hire.
Cheers
Ian