Share your experience!
That key shows up in my notification bar usually when running a VPN app, which means my connection can be monitored by others.
Do you have some kind of adguard? Perhaps your network is monitored somehow.
Try to boot in safe mode and see if the same occurs.
@Christofer Something like this:
http://forum.xda-developers.com/z3/help/random-key-icon-status-bar-t3086815