求翻译：9、看标识。有的正规的零部件上标有某些记号，比如正时齿轮、活塞顶部等装配标记，用来保证机件正确安装，没有的不能购买。是什么意思？

9, see ID. Parts marked with some of the existing formal notation, such as timing, like tags at the top of the piston, used to ensure the parts installed correctly, cannot purchase not available.