Word for "seeing without being seen"

Is there a word for seeing without being seen? I want to write about those on the advantageous side of tinted glasses. Visual/optical eavesdropping is the closest phrase I can think of.


Try covert, as in covert surveillance, or in your example, a covert observer.


I'd probably go with spying:

to watch secretly usually for hostile purposes


Does incognito work for your purposes?

: with one's identity concealed