What the "NP" reading means for a DVI computer monitor?

After falling down a pretty deep internet rabbit hole - It seems that its the polarity of the sync signals - in this case a VESA Signal 1680 x 1050 @ 60 Hz timing. These seem unique to a specific set of refresh-rate/resolution/standards, and arn't of particular use to the end user. They're handy if you wanted to make a microcontroller (say in a toaster) output VGA I suppose, or had to set up some interface by hand.

The NP listed in your monitor's menu setting option stands for Negative/Positive input signal polarity. Other input signal polarity settings that you'll see are NN and PP (for Negative/Negative and Positive/Positive, respectively).