盖印

例句：

1. 1. The official document requires the signature of the president for approval.
   官方文件需要总统的签名批准。
2. 2. Before signing the contract, they reviewed all the terms and conditions.
   在签订合同之前，他们审查了所有条款和条件。
3. 3. After receiving the letter, he immediately signed it and sent it back to the sender.
   收到信件后，他立即签字并寄回给发件人。