Nikon COOLPIX P510 Reference Manual page 59

The Playback Menu
01 Protect
Press the [] button (Playbackmode) ") MENU b utton (_13) -) O-_Protect
Protect selected pictures from accidental deletion.
In the image selection screen, choose a picture and set or cancel protection. See
"The Image Selection Screen" (_59) for more information.
Note, however, that formatting the camera's internal memory or the memory card
(_85) permanently erases the protected files.
Protected pictures are recognized by the @_ icon in playback mode (_10).
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