Drum roll please...
I got a reply from the creator Rory O'Connor:
"We are always reluctant to say what the images on the cubes represent. We like that there is some uncertainty involved. As for your sugestions, it's all of those things! It might also be a ticket, license or ID card. The meaning will change depending on who is using the cubes at that moment.
I hope that this is an acceptable answer.
p.s. if you REALLY must know, I will tell you what I was thinking when I drew it.
"
I REALLY needed to know
:
"Oh, ok then.
It was meant to be a credit card. But I left it generic enough to mean other things, as you have discovered."
Well done zm!