If it is only valid from the perspective of signature, because the front part has the same legal effect as the seal and seal, but it also depends on whether it is the appraisal opinion made by the unit. If it is in the name of the unit It must be stamped, and if it is in your name, just sign.

According to the "Interpretation II of the Contract Law"

Article 5

If the parties conclude a contract in the form of a contract, they shall sign or seal it. If the parties concerned press their fingerprints on the contract, the people's court shall determine that it has the same legal effect as a signature or seal.