Samsung 275TPLUS - Manual (Page 39)

OSD Lock & Unlock
When pressing the AUTO or PIP button after locking the OSD
When pressing the MENU button after locking the OSD
Menu Description
Locked
This is the function that locks the OSD in order to keep the current states of
settings or prevent others from adjusting the current settings.
Lock : Hold down the menu button for more than five (5) seconds to activate the
OSD adjustment lock function.
Unlock : Hold down the menu button for more than five (5) seconds to deactivate
the OSD adjustment lock function.