Hello, the establishment and effectiveness of the contract requires the consent of both parties. Only one party signs it, and the contract is not established. According to your description, I can introduce the following two possibilities:

First, you sign the original contract, and others take a copy of the signed contract before signing your name. Such a contract is invalid.

Second, a contract, take it and make two copies. You sign one of the contracts that you think is the original, keep it for yourself, and sign the other contract that you think is the copy. Such a contract is valid in form, that is, it has legal effect. !

Thank you, please adopt what you think is good!