Zapper is the way to go
Had a van to remove - three layers of reflective vinyl installed in 1995 and brittle as anything. Tried all the usual routes and a few non-conventional (read - chemical) routes with poor results and wasted time.
Borrowed the snap on version of this tool from my buddy who has a body shop (he never even realized what the funny looking rubber wheel was for - they only used the wire wheels for frame work). His was air powered and a real match for my small compressor. After removing 6 letters in 5 minutes CLEANLY, I put the tool down and went online to order the electric MBX Zapper next day air.
When I got it in hand, I went at the van, cleaned off ALL lettering and adhesive (even with that metallic reflective dust in it) PERFECTLY and even buffed out the paint.
As far as cleaning off the dust left behind, foaming glass cleaner (non-ammonia of course) and a cloth rag - wipes right off with no residue.
I have also used it on a few de-commissioned pieces of fire apparatus and chiefs cars before being sold. Never had a vehicle yet that took me more than 2 hours (even the worst reflective striping and gold) - never once had a concern about using it on any vehicle regardless of age or type.
I have even had occasion to use it on a BRAND NEW BLACK FORD VAN after my assistant put on a VERY LARGE uh-oh. NO ISSUE WHATSOEVER.
Used it on my own boat and it burned a bit, but was being covered over again so no big deal. (I wouldn't use it on a customers boat though).
This was a tool WELL WORTH the money.