On FB your photo is used as your ID when you play games so many women "hide" behind either their children's photo or a cartoon character. Unfortunately there are a persistent number of chancers who want you to talk dirty on the chat board or make unwanted personal remarks about your appearance. It is also a signal to other mothers that you can just play a quiet game with them with no hassle, so is a useful code.
This is very true also, i have found this to be very much the case. It reassures other people that you're not strange, or about to start inboxing them inappropriate messages