请你在这里签个字。

Qǐng nǐ zài zhèlǐ qiān gè zì.

Please sign here.

请在账单上签名。

Qǐng zài zhàngdān shàng qiānmíng.

Please sign the bill.

明天我们要签订合同。

Míngtiān wǒmen yào qiāndìng hétong.

We will sign the contract tomorrow.