It looks like being etched into the glass

or it is a trade-mark of Nikon...没idea这是啥东东：（（甚至觉得不影响照相

Good to know每个镜头都有特点，You have owned many.

俺的问题是不知道是牛还不牛：（（管它的，不忘自己是谁就好：）