Instead of 3Dprinting a sign base, I used 3 Lego pieces as base for the 0.2mm thick sign.

Attached OpenSCAD file allows to easily create the numbers/texts on  top of sign you need.

Forum posting with more details:
https://forum.prusa3d.com/forum/english-forum-general-discussion-announcements-and-releases/single-layer-3dprint-to-create-numbered-signs-for-testing-autofocus-camera/