Unknown symbol in BlackBerry screen

[jccanet]

Hi all,

I have a Blackberry 7100v from Vodafone Spain, some weeks ago an unknown symbol appeared on the screen ONLY when I lock the keyboard. It's located on the center of the upper side of the screen (just under the Bluetooth symbol) and it consists of a "2" and something like a check symbol inside an square.

Do you know what it is?

Thanks in advance and best regards