its next to the texts icon on the right. it looks like it is something to do with the browser. I honestly never seen it before. I looked in the manual and it showed every other icon besides it.
usually you get it if you are browser the web and then lose connection (radio shut off, no service etc) it will save that request so you can then use it when you get your service back and resume were you were. But you can reboot or close the browser and still have it since its saved as a message.