I believe it means "reboot your phone" or "power-cycle your phone". It's an icon of a power-button with a recycle arrow. It's likely caused by a configuration change that was made (or at least the firmware thinks one was made) on the web interface. If you have an OBI ATA, you'll sometimes see a yellow triangle with a ! in it, on the web page, indicating the same thing: reboot needed.
Does it go away if you reboot or power-cycle the phone?