lThis is an OpenSCAD design for sign letters, to be lit with commonly-available adhesive RGB LED tape (specifically this stuff from BTF-Lighting on Amazon, though any similar tape is probably compatible especially with parameter adjustments). I've provided STLs sized for my Sovol SV06 Plus, but it's easily adjustable to your printer size - the “size” parameter controls the approximate height of the letter in mm, although it'll usually undershoot a fair bit so you might need some trial and error. Make sure your first layer squish is well-tuned, maybe even a bit over-squished, since the bottom of the print forms the face of the letter and is necessarily thin (sized for 2 0.025mm layers in the provided STLs) - the only letter I managed to print in time for the contest (shown) has some pretty obvious lines in the front, which would not be the case if the Z offset was properly set. Oops. Anyway, provided STLs use Baskerville but it's easy to change to whatever you want, though the design will work best for things with a consistent outline.
There's also a backplate for each one that pressure-fits into the letter, which adds to the reflectivity and durability, and you can of course glue it if you like. You'll need to cut a hole somewhere for the wires, either in the slicer or with cutters IRL - I didn't do that in the provided STLs as it'll be dependent on how you want to install them.
The letter in the photos is printed in Polymaker White ASA, which prints great without an enclosure for me, as long as I use a draft shield.
Update 2023-7-11: Version 2! Changes:
Old versions are available in folders marked “(OLD)”, files in the root and letter_v2.stl are the new ones.
Update 2023-07-10: Updated the .scad file - no geometry changes, just cleaned up and added some comments.
The author marked this model as their own original creation.