Motorola v66

My Motorola V66 displays a letter G with a squre round it, on the screen just to the right of the clock. I have had the phone for about a year and a half but it has only displayed this 'G' for the last 3 days. I can't find anything in the manual to tell me what this means. I know it is nothing to worry about as the phone seems to work OK but I just wondered if anyone could tell me what it means.

Thanks,

Ross