It's definietly a new message from app world. Wether it's an update or not I don't know for sure. I started a thread about this a while ago...you can view it here. It's contains the fix.
It will also show up in your messages list.
It's the icon that is telling you that one of the apps or more that you downloaded from the App World are now available for updates.
To see you can either go in messages and it will show you and clicking on that message will take you directly to the App World or you can simply go there to start off with.
I tried clearing all messages and checking for all app updates and still nothing. I downloaded the new version (which i already had) of app world and that finaly got rid of it. thanks to everyone.