You might want to hit it with Krylon crystal clear or workable fixative to stop the sticker curling prior to the acrylic seal. In the event you are paid a Starbucks wage, you can always substitute hairspray.

The acrylic sealer (even if you wanna get fancy and use something like one of Liquitex's acrylic mediums like gloss or matte) should ideally do the trick on the ornaments, but for a sturdier hold you'll want to bond them further with some simple Elmer's school glue on the underside before layering the seal/medium over them.

everyone at my store uses clear nail polish (-:

I always just use Mod Podge and it seals it

Everyone at my store puts clear packing tape on their nametags since it's always in the store anyways

Let us know how it works out!