Used when a group of people are sneaking around outside in the dark, for example trying to steal something from someone's back yard or throw rocks at cars, and someone spots a person coming who is not of their group; they either yell FENCELIGHTS loudly as a warning and everybody runs like hell, or they can secretly whisper it or transmit it over 2 way radio so everyone can clear the area stealthily. Similar to the common "five-0" but is used to indicate someone who doesnt know what theyre looking for, such as an innocent passer-by. Used among people formerly and still of several Edmonton (Canada) area high schools.
Etymology- When us friends were going through some guys shed, when a car came we were in plain view and the only warning of this was car headlights shining off the fence; and from then on there and everywhere else it came to be known as Fencelights.
Fencelights!!!! Everybody get the fuck out!! (everyone runs to a safe spot)