"用勾作为记号" can be translated as "use a check mark (✓) as a symbol" or "mark with a tick" in English.
Here are a few examples of how this phrase might be used in a sentence:
* Please use a check mark (✓) as a symbol to indicate your choice. （请用勾作为记号来表明你的选择。）
* Mark the correct answers with a tick. （用勾标记出正确答案。）