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.

请你在这张纸上签个名字。

Qǐng nǐ zài zhè zhāng zhǐshàng qiān gè míngzi.

Please sign your name on this paper.