"Winger" is used as a closing in a letter, and is an abbreviation of "Your Wingman" which implies a pledge of both
friendship and fidelity by the sender. Similar to the use of "
Huckleberry" in the phrase, "I'll be your
Huckleberry".
When used as a goodbye between two people, i.e. when "Winger" is spoken, it is common to gesture by forming a "W" by holding both hands up in front of you at chest level, extending only your thumbs and pinkies, and putting both thumb tips together so that it looks like a "W".