This is equally common in China, and it is purely reflexive. Even I have to resist throwing the “V” when I see a camera. There are also a few variations- the gun/camera frame, etc.
Asian photo culture is pretty interesting and notably different than our own.
Self-portraits are the way to go. People- especially young women- will gladly show you 100,000,000 photos of themselves. They don’t do a lot of the “my friends acting wacky” or “documenting my family party” or “famous stuff I saw but am not posing in front of” that we’d expect. It’s mostly about the self portrait. Even travel photos are “me in front of a museum, me in front of a statue, me in front of the ocean” etc.
Furthermore, these portraits are often of the “glamor” variety. A picture of you smiling happily in front of the Eiffel tower wouldn’t be enough. You’d want to be posing in a white dress holding a rose and looking wistfully into the distance. Or smiling softly into the camera wearing a floppy hat and clutching a giant teddy bear. Or laying in the grass pretending to read a book while the wind artfully blows your hair. It’s not just “I was there.” It’s “I was beautiful there.”
Indeed, collecting these glamor photos seems to be a pretty common purpose for travel. Any Chinese tourist attraction is going to be full of young women in their best clothes posing as their sheepish looking boyfriends click thousands of pictures. Many of my students will consider “taking pictures of myself” to be a good weekend outing, and the richer ones will spend no small amount of money on professional photos on a regular basis. Beauty and image are, in my experience, much more important to young women in Asia.
I always thought this was a reason behind the peace sign- in this culture photos are supposed to be about people and they are supposed to be posed. So should you be caught without your rose or floppy hat, the peace sign is the least you can to do make it known that you care enough about your image. It wouldn’t do for people just to be taking pictures of you doing whatever. You want to at least be projecting something, even if the “I’m young and wacky and getting my picture taken aren’t we having fun!” peace sign is all you can manage.