How is a vigilante with a LN social identity and a NE vigilante identity not LE?

[Zhentarim]

Also, what are some things this vigilante could do that are unmistakably NE without creeping out the rest of the party?

I like the mechanics and flavor of multiclassing into the evangelist PrC with Mammon, Archdevil of Greed, as my patron. Flavorwise, I'm a greedy chef who makes lots of money as a famous cook, and they travel with the mixed-alignment party as their chef...but they also have a darker secret identity as well that takes care of the darker/edgier stuff the party wouldn't normally do, maybe even with the warlock subclass or the serial killer subclass.

Also, what are ways to more clearly delineate my LN social identity and my NE vigilante identity?

[Sir Edgen]

Well, I'm pretty sure that for a "standard" vigilante his NE persona is just it - a persona. He may act like NE, but deep down he remains LN. Basically, persona is an advanced magical mask that gives him another "alignment" to prevent finding his true identity. It isn't a dual personality or another side of his true self

[Saintheart]

Flavorwise, I'm a greedy chef who makes lots of money as a famous cook, and they travel with the mixed-alignment party as their chef...

Also, what are ways to more clearly delineate my LN social identity and my NE vigilante identity?

I present your go-to character sheet for your guy:

https://theawesomedaily.com/wp-content/uploads/2017/02/gordon-ramsay-memes-7-1.jpg

[Zhentarim]

I present your go-to character sheet for your guy:

https://theawesomedaily.com/wp-content/uploads/2017/02/gordon-ramsay-memes-7-1.jpg

Noted!

Their Serial Killer identity could leave a dish prepared from the victim's remains, maybe.