TL;DR They’re not dice.

The computer-designed objects called trajectoids follow a predetermined path when rolling, and usually look somewhat like peeled potatoes.

I haven’t seen a trajectoid with an obviously arbitrary, complex path, such as someone’s signature (as opposed to demos of epicycles), so there may be limits to what lines can be made.

I think the similarly-looking gömböcs are cooler: convex, uniform objects that always return to one stable orientation when laid on a flat surface.