I can verify, with and without a computer, now and till the end of time, that "5885893a033d01aab4d337375a740c043a8a6241e868873084342a658c3f924c1e43a140111025fd8b5f6a8135f1d077c9fd6c80958834681615bb60be12069e" is a valid signature by "9aff936f8619411c0692e14d7aaf49e45cfd908e8a9c7afd3c72a64ba0dcabfc" for note 3002d0906592f1f372bfedfc0c61c5e770c2a37e7c84d4f267edc8995f544229 (the one I'm replying to), meaning that the owner of that npub authored (you) authored that post. 

I don't have to rely on a central authority for that, a relay owner CANNOT submit a note and pretend you sent it, no matter how many resources they have (let's ignore quantum computers, once they become actually real (and I mean actually usable) nostr can easily switch to a quantum resistent algorithm and apps can display warnings over non-quantum signatures).