What two conditions must a digital signature meet?

Legibility and neatness are physical handwriting qualities and have no meaning in the context of cryptographic digital signatures.

A digital signature must be unforgeable, meaning no other party can produce a valid signature that appears to come from the legitimate signer, and it must be authentic, meaning the recipient can cryptographically verify that the signature was produced by the claimed sender. These two properties rely on asymmetric cryptography where only the private key holder can sign, while anyone with the public key can verify. Together they provide non-repudiation and integrity assurance.

Uniqueness and special characters describe password complexity policies, not the cryptographic requirements of a digital signature.

Character length relative to a physical signature is a nonsensical metric - digital signatures are fixed-length hash outputs determined by the algorithm, not the physical signature.