This is what the Macrovision copy protection signal on VHS tapes looks like. When the boxes are full white it causes the picture on a connected VCR to darken. When they flash, the copy flashes light to dark. When a VCR is hooked to a DVD recorder, the squares tell it not to go into Record mode. Boxes that let you get around this work by placing black squares over these.
Laserdiscs could not have Macrovision since this space in the VBI is taken up by time code. There is no native vertical interval on DVDs, but all DVD players are equipped with Macrovision through their standard video outputs- a flag on the disc tells it whether or not to turn on the signal, and it also appears as similar squares in the player's vertical interval.