Flight Mode Icon
The CEA (Consumer Electronics Association) once tried to create a standard icon for the industry to indicate when a device is in "flight mode".
See: Flight Mode
If manufacturers used the standard icon, it would make it easier for flight attendants to verify that devices are in flight mode.
As of early 2017, manufacturers have generally not adopted this standard icon, using a variety of non-standard icons instead. It is not clear that it will ever become widespread.
CEA guidelines state that the icon should be accompanied by the words "transmitter disabled" when possible. There is also a standard icon for when the phone is not in flight mode, which should be accompanied by the words "transmitter enabled".