[Charlie]

What was he cursing about while he was signing it? Because it was a replica? And he signed it anyway?

I don't think any of the standard clear coats are going to last over vinyl. You might try artist's "fixit" spray which they use to put a protective satin coat over pencil drawings to prevent them from smearing. Not sure if it has any uv protection, but it should give some protection without being obvious its there. You will have to experiment first on a spare piece of vinyl to see if "fixit" spray is impervious to Armor-All.