our Signature is represented as:

pub struct Signature {
    public_key: PublicKey,
    payload: ConstVec<u8>,
}

but in the case that we know who's signed the message having public_key in the signature is unnecessary. It is unnecessary because the verifier still has to know what public key it expects in the signature. I noticed this due to the fact that we require a key pair to sign genesis. In that case there is only 1 signee and there can't be any doubt as to what public key must have been used.

Another example is the consensus. We don't have to send full blown public key with every signature. Since all nodes have to agree on the topology I think it is sufficient to just send index of the node in the current topology

I'm not sure what we can do with MST