Both are OK. Both parties or parties to a contract or agreement can freely agree on the conditions for the validity of the contract or agreement, including seal only or signature only, seal plus signature, signature plus authorization letter, etc. The parties may not only agree on the form of the contract as a condition for its effectiveness, but may also agree on a certain time limit or special circumstances as a condition for its effectiveness. Article 490 of the "People's Republic of China and Civil Code" Where the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign, seal or fingerprint the contract. Before signing, sealing or fingerprinting, one party has performed its main obligations and the contract is established when the other party accepts it.