This is a custom watchface for the Pebble smart watch. Download it.

It looks like this:

Although it may not be immediately apparent, there are 4 large numbers on this face. It works by having a background of lines going one direction, while another layer has lines in the other direction. The number digits change the direction of the lines.

Thanks to RichardG for the assets. Based on the Kisai Optical Illusion watch from TokyoFlash.