BR?
From Euphro
Another standard that is yet to be identified is that of the qualities that a Brasilian player looks for in another player before approaching him or her with the question. Some players do, in fact, add the tag "_BR" to the end of their in-game names to declare themselves "BR", but many players seem to pay this little mind when choosing which players to question. Whether there truly are guidelines that Brasilian players keep a lookout for, or whether the selection is completely random, remains one of EuphRO's greatest mysteries.
Other Uses
English-speaking players sometimes use the question to avoid other English-speaking players, particularly those reffered to as "n00bs". A typical use of the phrase in such a tactic would come after the "n00b"'s attempt to conversation with the escaping English-speaking player, leading the escaping player to try to pass of as a Brazilian player in order to avoid the "n00b".
BR
The combination of the two letters (typically capitalized but not necessarily so) without the question mark is a noun that reffers to a single Brasilian player. The plural of this noun, according to English-speaking players, is BRs, although the Portuguese equivalent ,yet to be reported, is theorized to be different.
Example:"Yeah, some BR owned me in Battle Dome."