标记符

例句：

1. 1. The engineer used a marker to mark the spot where the pipe should be installed.
   工程师用标记器在管道应该安装的地方做了标记。
2. 2. The teacher marked the test paper with a pen.
   老师用笔在试卷上做了标记。
3. 3. The chemist marked his samples with different colors for easy identification.
   化学家用不同颜色标记他的样本以便容易识别。