Years ago, I prepped decals for the folks over at The Bolter And Chainsword (http://www.bolterandchainsword.com). One of those was an adaptation of the 'gothic' numbers used by various sub-factions of the Imperium of Man. This past year, I've moved from decals to 3D printing. Why not adapt one of the more useful decal designs I did?

Note that the decal file is certainly showing its age. While it prints fine to a laser printer, importing it into TinkerCad showed just where my Illustrator skills were at the time.

These are intended to be used in conjunction with other 3D model parts, rather than on their own (although you could print them on their own for vehicle markings).

Each number is roughly 40mm square x 10mm tall. For comparison, Space Marine shoulder pads (at least when the decal file was designed) usually have an 8mm diameter face, while their knee pads have a 5mm diameter face.