What does Tor signature mean?

Where is the Tor signature defined? What does it mean that the internet censorship devices recognize the Tor signature?

Thank you.

Tor’s key derivation scheme. This explain how Tor relays get a keypair for signing.

Thank you so much for your reply.
Why isn’t this made stealthy so that censorship devices can’t easily detect the Tor?

There is a fundamental issue that limits how stealthy it can truly be. This is because the IP addresses of Tor relays need to be publicly known so that clients can connect to the network in the first place.

Every Tor client needs to download a full list of all relays from a directory authority or it’s mirrors, and the fingerprints in order to build circuits. Even if the key fingerprints/signatures were somehow disguised, censors could still block connections to known Tor relay IP addresses trivially.

Since relay IPs must be public for the network to operate, there is little benefit to extensively obscuring the key fingerprints. Censors would still be able to detect Tor traffic based on destination IPs alone.

Therefore, there is no “need” to try and obscure the keys for Tor relays.