Well, I'm not sure. Looking in the back of the manual, there is a fold out that tells you what all the little icons mean. And the one I have is just the regular orange folder which means "unread message." I'm assuming that means email?
Edit: Ok, I guess it was just a glitch. I took the SIM card out and put it back in, and now the message indicator is gone. Hehe, I should have thought of that first since that seems to be the fix for a lot of things in the past. Kind of RIMs version of rebooting Windows.