Because of the comma placement's ambiguity... perhaps intentional... it depends on how you read it. It could be a taunt, addressed to the person who would have liked to find the contents... or this could be the signature of the one who removed them.

[He stares, shaking his head.]

"N.P." Could be the "Japanese Police," but. That, I doubt.

[If only because they could never beat L to a conclusion or a discovery, not with a head start of a thousand years.]