My cell phone when its keypad is locked (so that it ignores keypresses) displays a small picture of a key on the display. I find it rather confusing - IMO it should be a picture of a padlock which is just the same recognizable but indicates that the phone is "under lock", not "somehow related to a key".
I'd like to know why using a picture of a key could be advantageous in this scenario.
Why would one prefer using a picture of a key over a picture of a padlock to indicate that a device is locked?