They all say "Dimarzio, made is USA", some have individual markings but most only have markings saying the're dimarzios.
You should really be able to tell by playing them, especially the
air norton, youll notice right away how clean it is compared to any stock pups.
Still the easiest way would be by asking to give you the boxes aswell, which they should do but some dont. Specifically ask for the boxes and warranties etc.