inner mark

例句：

1. 1. The company uses internal marks to indicate the location of different departments.
   公司使用内部标记来指示不同部门的位置。
2. 2.The researcher found an internal mark on the ancient manuscript that could not be explained by any known technique.
   研究人员在古手稿上发现了一个无法用已知技术解释的内部标记。
3. 3.The map had been marked with internal marks indicating the direction of travel.
   地图上有内部标记，指示了旅行的方向。