I think it could be binary. Note that since 5 is 101 in binary the representation is strictly 0101. Perhaps the image is trying to represent the old tick-a-tape, (?), that use to be used with squares cut out to let the light through.

I agree - binary was what I decided. I think my brain didn't like associating black with 1 and white with 0.

I showed the clock image to my further maths students this morning and they enjoyed figuring it out. One of them even managed 3, purely because of an off the cuff remark I made a couple of weeks ago about why 'dx' is written at the end of an integral! I had to explain 1 and 8 though.

Ah, very nice! I find things like that quite mesmerising. My parents had one of those chinese ball clocks when I was young, which always intrigued me. You are right.. plenty of questions they could ask!