Harper Pin?

[G_Admiral_Thrawn]

Why did the devs (and how do you know) limit the Harper Pin to just Jahiera, ESPECIALLY since the item description says anyone could use it (it's not limited to Harpers), but it's given only to Harpers.

[Nythrun]

It's mind reading you're asking for, but:

 

Signature items are just for more NPC distinctiveness - since you spend much of the game in nuisance combat with bandits, anything that makes NPC01's bandit-killing a little different from other folks' can have a large cumulative effect. And if the PC could use them some players would be likely to festoon <CHARNAME> with everyone else's heirlooms, and they didn't like that idea.

 

It's just a design decision, and one that's common to many rpgs.