I'd worry for Mac Fleetwood, the first time he runs into Doorman and asks him to stop by the Mission.

 

By smell.  She remembers very well what Doorman smells like because she was rather close to him.

There are external factors and personality-based choices where the two Jay's would differ, like using different kind of shampoo or laundry detergent.  Presumably, being a less agressive personality, maybe the Hatman Jay uses a more flowery shampoo, or Doorman uses a slightly stronger aftershave.  That's the kind of thing Liu Xi would notice, but his own teammates never would.  Especially because she has a lot of emotion riding on that decision - a hint of Doorman's smell would make her fearful and angry.

Of course that in no way makes Liu Xi unique.  It's quite likely Zdenka would notice it too (though since she doesn't associate harm with the smell, he could just tell her he changed shampoo - and since she doesn't see him every day she might believe it).  Even more so, since she's part wolf.  And Doorman would have to avoid Glory probably too, since Glory sees the real Hatman daily and knows the smell.