HMAC is a Message Authentication Code (MAC), not a cryptographic signature. The key difference is that anyone who can verify a MAC could also have created it,

HMAC is a Message Authentication Code (MAC), not a cryptographic signature. The key difference is that anyone who can verify a MAC could also have created it, whereas with a signature only one entity could create the signature but anyone at all can verify it (the public key is public). MACs therefore allow repudiation of the authenticated data (one party can claim that any other party with the shared key created the MAC), while signatures prevent that (only the holder of the private key could have signed). They're related, in that they both provide message authentication and integrity, but otherwise quite different constructions.