Japan's fondness for this pose is well known around the world — or at least any spot that attracts Japanese tourists.
The Peace Sign in JapanThe peace sign began to appear in Japanese photographs in the late 1960s. At the time, the peace sign was part of the hippie movement in the United States. It was a symbol of opposition to the Vietnam War.
Japan also had a hippie community in the late 1960s who were known to frequent the Shinjuku area. The use of the peace sign in Japan began within this hippie subculture.
From Hippies to Mainstream Japanese CultureHow the peace sign made the jump from the hippie subculture to mainstream Japanese society isn't known. Urban legends link it to a popular American figure skater (Janet Lynn) or a 1972 Japanese Konika commercial.
Whatever the spark — beginning in 1972 it was popular amongst Japanese youth to pose for photos with a peace sign.
Peace vs CheeseThe peace sign photo pose is often compared to the tradition of saying "cheese" before a photo (in the English speaking world).
Saying "cheese" for a photo tends to make people smile. In Japan, the peace sign has become a visual "cheese" — a cue to the photographer that you're ready for the photo. Like saying cheese — it seems to make you more photogenic somehow.
These days, the V-sign is made at various angles of the hand (e.g. palm in or out). Such gestures aren't meant to have a meaning — it's just a photo pose.
It's ContagiousIf you visit Japan you may find yourself giving the peace sign in photos. Virtually every tourist to Japan does it. It's often done mockingly at first — but it's addictive.
The V-sign pose is also common amongst fans of Japanese pop culture (e.g. cosplayers).