watch that doesn't appear to tell the time in any way but that the wearer can tell with

-a color gradient with four corners
the four corners are the four digits of the time
use hue to express digits, or possibly hue and brightness. primary and secondary colors alone make 6 colors. + white and black make 8.

-a blank face, or something that's obviously not animated
use oled's in the shape of company logos, fancy trims around the watch face, etc., that can change color to show time

-pictures that change every minute. clues in the picture can be used to count time. e.g. 5 people in it = 50 minutes

-random dot stereorgam to show the time

-picture stereogram but the picture is just an abstract design