4 sentences

1. 他在这份契约上押了一个记号。

   tā zài zhè fèn qì​yuē shàng yā le yī gè jì​hao.

   He made a mark on this contract.

   Source: Dong Chinese Dictionary

2. 他在那页书上折了一个角做记号。

   tā zài nà yè shū shàng zhé le yī gè jiǎo zuò jì​hao.

   He folded the corner of that page as a mark.

   Source: Dong Chinese Dictionary

3. 农场主在牛背上烙了一个字作为记号。

   nóng​chǎng​zhǔ zài niú​bèi shàng lào le yī gè zì zuò​wéi jì​hao.

   The farmer branded a character onto the cow's back as a mark.

   Source: Dong Chinese Dictionary

4. 这种数学记号在教科书中非常常见。

   zhè zhǒng shù​xué jì​hao zài jiào​kē​shū zhōng fēi​cháng cháng​jiàn.

   This kind of mathematical notation is very common in textbooks.

   Source: Dong Chinese Dictionary