significance of white padlock symbol on screen

Hello, can anybody help, I have looked all over manuals internet youtube, etc in vain for answer
I have several Nexus 7 tablets, on some I notice when starting , Google appears in white text and a white padlock at bottom of screen, however on some the white padlock symbol does Not appear. ( this occurs during initial start as first indicator on screen)
Anybody know the significance (or otherwise) of the padlock symbol...

This is NOT the padlock to unlock that appears following boot sequence

Many Thanks Geoff

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