1. Fraudulent use of other people's signatures may constitute the crime of forging documents under illegal circumstances, and it involves infringement of other people's rights. If Party A uses Party B's signature to sign a contract with another party without Party B's consent, then this behavior is illegal.

2. If it is legal, for example, Party B authorizes Party A to sign and let Party A carry out relevant activities on its behalf, then this behavior is legal. In this case, Party B shall sign an authorization agreement with Party A to specify the authorization content and terms.