Anonymous Brazil released several videos in support of the movement and because previous Anonymous activity, Occupy and the Arab Spring were models/antecedents, they used the V For Vendetta Guy Fawkes mask. To a lesser degree, the participation of bonafide anarchists in organizing the initial protests also played a role in the masks being adopted early on.
[youtube] http://www.youtube.com/watch?v=zSdV176fI7g [/youtube]
Most protesters seem to have no idea what the masks represents, or may vaguely remember the Hollywood film. So as the protests have marched on, all sorts of splinter protests with widely different demands have popped up, or seized the existing unrest and discontent with their government to attempt to advance their own agenda.
One of these has been a call for a return to military rule–Brazil was under a military dictatorship from 1964 to 1985. These "protesters" keep using the masks, as they have become identified with the original protests and help them remain anonymous.
I think you can guarantee the people in the picture below are completely oblivious to the immense irony of calling for a return to a military dictatorship while wearing the V mask.
Another, interesting bit about the original protests, in the first week they were sometimes referred to as the "V de Vinagre" (V for Vinegar) movement, after a video of a protester being arrested for carrying vinegar went viral…
And even a game…