Well, having played with this for years, here's what I know:
There is signage vinyl designed for inkjet printing, white, clear, maybe other colors. Anything that is a freestanding shape would work, but no metallics. I've knocked off the round ttt stem decal for instance. But inkjet is waterbased inks. And when they talk about archival they mean displayed in low light situations like artwork, not in the direct sun.
The ALPS is an amazing printer, white, metallics, cmyk, but they were discontinued. They claim they'll offer supplies for 5 years however. The frames I've done with decals from it seem to hold up fine under Imron clearcoating. Without, the decals are fragile, easily skratch and solvents will disolve.
Simple stuff can be done at a sign shop with a Gerber. Individual cut letters or printing in colors on vinyl. Can also be computer cut in complex shapes. Set-up charges make it expensive if you're not doing a number of pieces.
But the biggest drawback to all this is the time it takes to create the a rtwork. This is not a click and you're done deal.
Ted Williams