streak = 斑纹

It means that whoever cleans the glass/windows does not leave any dirty marks on it. I use methylated spirits and a scrunched up newspaper to clean my windows/glass table/mirrors. No streaks!

Means the surface has no dirty marks left by the cleaner. A streak can mean a mark, easily seen on a shiny surface.

If you don't know what that means then I'm not going to let you wash my car!