The High Isle prologue quest has at least three NPCs with Signature Styles.

We could see the Nibenese Court Wizard Style, Windhelm Scale Tunic Style and the Knight of the Circle Style on NPC. I didn't identify Valessea's outfit, I guess it's a costume.
I find it really nice to see such unusual styles. I thought only players would wear them although it is quite rare to see them. Either because the style is too rare, too expensive, limited time to acquire or there is significant competition between styles.
It would be cool to see NPCs with Events Styles. I don't believe it exists today.