IMHO alignment has always been a "guide" on a characters behaviour and motivations. It lets the player know what kind of decisions a character would make in any given situation. Is the character more concerned about self or others? (good, neutral, or evil) Are they individualistic and chafe under rules or do they believe in structure and adhering to societal norms? (chaotic, neutral, lawful).
Concealing alignment is like trying to conceal the morals and behaviours of the character.
I think the real question is, how do you let other players and NPC's see past questionable morals and behaviours.
A charm spell comes to mind...
There is a nondetection spell that makes it impossible for anything less than a 9th level divination from working on you.
I oddly had a dagger of nondetection once. I think that was galarion tho.
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