Should a command like this take in to account what generation you're searching in or just show when a user had an exclusive move?
Yes, I personally think that signature moves with 3 or less distributions would count as signature moves that can be searched using an exclusive command such as:
Bolt Strike Zekrom & Victini,
Fusion Flare Reshiram & Victini,
Night Daze Zorua, Zoroark & Lunala, etc.
As for moves like Mystical Fire and Darkest Lariat, I would not count those as signature moves in Gen 8 in the regular
/ds signature. Doing
/ds6 signature however, should ideally display Mystical Fire as one of them. Likewise,
/ds7 signature should display Darkest Lariat whereas it wouldn't in Gen 8.
Also, great suggestion, I think it will be very useful to be able to view the actual distribution of some sig moves such as the aforementioned Victini which shares these distributions with Zekrom, Reshiram, and Kyurem.