adj.无标志的，无标记的，无记号的，无人盯防的

The unmarked police car pulled up to the scene of the crime.
无标记的警车停在犯罪现场。
She received an unmarked package in the mail, unsure of who it was from.
她收到了一个无标记的包裹，不知道是谁寄的。
The doctor prescribed an unmarked pill for my headache.
医生给我开了一粒无标识的止痛药。
The detective's unmarked notebook contained crucial evidence.
侦探的无标记笔记本里有关键证据。
The unmarked signpost led us to the hidden trail.
那个无标记的路标指引我们找到了隐藏的小径。
The airport shuttle is usually an unmarked van to avoid attracting attention.
机场接送车通常是无标记的面包车，以避免引起注意。
The unmarked grave of the unknown soldier is a symbol of honor.
无名战士的墓碑象征着荣誉。
The unmarked building served as a secret meeting place.
这座无标记的建筑是秘密集会的地方。
In the dark, she couldn't tell if the house was unmarked or not.
在黑暗中，她分辨不出房子是否有标志。
The unmarked text file contained sensitive information, so it needed to be encrypted.
这个无标记的文本文件包含敏感信息，因此需要加密。