It appeared after I installed the latest system update and I haven't got any joy from Google. The icon looks like a rectangle perched on it's smaller side (possibly a phone) with what look like signal bars coming from each side.
Resolved. My phone ringtone had been reduced to zero after the update and when I increased it the unknown icon disappeared. It was obviously alerting me to the fact that my ringtone was muted. I trawled Google and couldn't see that icon anywhere!
