As mentioned in another post, BigClive posted a video on creating letters that can be lit to build a sign. He used two simple OpenSCAD scripts for back and lid.
I always wanted to make those, but since doing this in FreeCAD and probably any other CAD would be over complicated and less flexible I dropped the idea. However I forgot about OpenSCAD and here is where it really shines. (got it?) 
The scripts I used can be found along with the Video in the description. You need to copy and paste the scripts into an editor and save them. Now you can load them into OpenSCAD and use the build in customizer or directly change the scripts. I preferred the latter, because you can save your settings along with the script and if you need to print a replacement cover, you have the values right there, with your project data.
My sign is work in progress and I need to go shopping today to get ABS for the front covers.
As you can see I connected the individual characters by using plastic bars. The lower ones are solid and the upper ones are U-shaped. These are ment to hide the wires inside. As you can see the snap on covers for the wire channels are waiting for the project to be finished. Those are not part of the original scripts. I designed them in FreeCAD.
This is considered to be a prototype, so the back side is not pretty, even so I gave my best. This image is from the finished lamp and as you can or can not see, the wires are now hidden inside. My quickly design channels work, but have some minor issues.
I printed the entire thing in ABS, which allowed me to weld the structure together using a brush and Acetone. The lamp is not a solid piece, but it can take a hit without breaking apart. The connections are as strong as the print and much more robust compared to using clue. That’s why I like ABS so much. If it breaks you use a Acetone brush, push it together and it is good as new. In fact even stronger at that point. Since all channel parts where just 100mm long I had to glue 6 of them together to get the bottom stabilizer bar. No problem with ABS. Other glue would have failed here in the stability department, while the welded ABS part on its own in the end was a solid square rod.
Here the finished wiring shown from the top. You can see the wire leave on the top left of the M. The lamp will get light blue covers printed in ABS.
And it even works. I used six cheap 30cm strips with 20 LEDs each for this first prototype. I cut the strip into matching peaces and soldered wires on to reconnect them.
As you can see the light defusing is far from perfect. This is because of the flat design of the lamp. Also keep in mind that it looks far worst on camera. It is quite okish when being looked at with the naked eye.
However, what did I lean from this prototype?
Well, LED strips and round shapes end up in a soldering and gluing hell. Also more depth is required to give the light “time” to spread more evenly when using a defusing material. I tried several defusing methods, but they all need more space to have a better effect.
My cable channels worked, but are far from perfect. Even so it took just 20 minutes to design them, I made them more fancy than required, which made them a little flimsy. So I probably will use a different approach for the bigger version.
In fact it will be bigger as I plan the lamp to be able to stay up right without any stand. I will also do some testing with a single LED at the bottom or maybe one top and bottom. I strongly need a working defusing solution for this as the wires and the sides of the LEDs would be visible. I also actually plan to increase the letter size from 120mm to at least 160mm. In addition to that I want to use NeoPixel, so I can change the colors. This also allows me to use transparent ABS as cover, which maybe is a solution to my light spreading issue.
So, this is all for now. Maybe you have your own idea for a cool sign. Keep in mind that modern fonts contain more than characters so you are not limited to them. This is the perfect project to start soldering and hot gluing.
There are arrows, question marks, hearts, all kind of symbols and different number styles.
