Judging by the number of people here who've noticed it in their friends I'd say it's probably due to malware. Take a look at the font of "facebook" in the imag

Judging by the number of people here who've noticed it in their friends I'd say it's probably due to malware. Take a look at the font of "facebook" in the images and compare with the header bar - 2 distinctly different fonts. Edit: Also notice that all of the accounts reporting seeing it on their friends are brand new users.