Some women like to wear sunglasses on their head to show the fashionable character. They will look cool and fashionable when doing this. The sunglasses are now regarded as the fashionable accessories which will absolutely make you look different and cool. If you want to look different, you could choose such wearing way.
I saw many people doing the same thing, not only women. Because normal sunglasses would dim the whole environment, when people wearing a pair of sunglasses goes to some place inside with darker light, he/she would feel it is too dark to have a clear vision, so he/she would take off the sunglasses or just wear it on head. It is also possible that people wear it on head for fashion. I saw this image in movie many times. But as you know, sunglasses are not only decoration accessories. Sunglasses could provide 100% protection from UV rays. It is better to wear them on your face to protect your eyes when you are facing strong sun light. Long term exposure to UV rays would probably burn the surface tissue of your eyes and it definitely increase the risk of cataracts.
Yeah, you are right. There are many people who are willing to wear the sunglasses on their head, especially the Russian people. Of course, there must some reasons why those people do that. As far as I know, there are three kinds of reasons. First of all, some people do not want to put away their sunglasses, namely, just put on their head, so that they can easily full down the sunglasses when they are exposed under the sun. You know it is much convenient for you to finish the act. In addition, some people put the sunglasses on the head just making the sunglasses serve as a hair bond to prevent the hair from covering the yes. In fact, some of them put the sunglasses on the head for nothing, namely, they just want to make them look more fashion. Hope my personal advice can help you.