webtrekker;134104 wrote: (Stickers? Decals? What's the difference?).
Stickers -British ......... Decals - American Same thing but different worlds.
Vinyl depends on what you are trying to produce. A decent grade CAD/cut vinyl for solid colour text or shapes, mirror image if fitting to inside of glass.
For printed images a vehicle grade vinyl which needs to be laminated for outside use or printed onto clear in mirror image and then backed up with white for inside glass, in both cases bear in mind that glass "sounds" as though it is clear but is not in reality. It is often viewed at an angle and reflections and the glass itself will reduce vibrance making it more difficult to read.
What sort of printer would you use for printed items? It needs to be a proper sign vinyl printer, not dye sub or domestic.
Stickers will bond more aggressively to the surface over time but can be removed more easily with the aid of a heat gun or hot water from a kettle, either of which will soften the adhesive. Any remaining adhesive may need removal with a proprietary cleaner.
Tell us how you are intending to produce them and I'll see if I can recommend suitable vinyls.