Through active or passive approval, a partner indicates that further advances toward anal intercourse will not be met with resistance. Active greenlight may come in the form of a verbal agreement that anal sex will ensue such as a vocalized "yes" or, in the case that the receiving party is mute, a nodding of the head. Passive greenlight is more commonly observed and relies of the absence of resistance to anal overtures rather than affirmative verbal confirmation.
After successfully placing two fingers in her anus, Robert knew he had the anal greenlight when Lacey did not protest.
When you are wearing a jacket zipped up all the way to the neck, with hands in pockets, waiting to kick the shit out of someone, as seen in the movie Green Street Hooligans.
John: Why the hell is that guy standing like that? Does he not know he's about to get the shit kicked out of him?
Steve: No you tosser! He's Greenstreeting. He'll beat the fuck out of that mick bastard.