I'm actually really disappointed this wasn't addressed with a fairly obvious "checksum" mechanism - Including the ":" in the center, and giving that it's own lenticular pattern, such that only when viewed from the right angle do you see the : and otherwise you just see numbers.

(I'm not sure if this is really plausible - Are the numbers close enough that that would actually work? If you're off to the right or left, or too high or too low, could you potentially see the : with a different set of numbers than intended?)

>Won't this show the wrong glyph if you're looking at it from the wrong angle?

Time is relative (to your height).

I suspect short people and tall people will likely disagree about what time is shown.

Hm, could that be fixed by covering it with a "privacy screen" (used to cover computer screens, basically a bunch of tiny parallel tubes (all-angle) or grooves (one-axis, probably best for this))? Then maybe a blur on top of that to increase the viewing angle again (though that might cut the light too much since it's not an active emitter)?