Here you go - SCS Forum

It's not that hard, as far as guides go, only the generic on the SCS Wiki explaining the basic model setup. Then you also need def files. You can also analyze original SCS content and go from there.

For anyone else searching for an answer, select the curb (make sure it's quads only, otherwise this won't work), unwrap, reset UV, select a leading face and select follow active quads -> length. You might need to manually match half the UVs if they get distorted.

Use Conversion tools that turn .tga into a game ready .dds

In your mod folder for signs, you have to tell the game to look for your atlas - def/sign/atlas/ca_91.sii for example. Look at original files for more info.

No you don't. It's preffered if the texture is unique to the object, but seamless textures are best left alone. Anyway, here's how to assign multiple materials to one object.

I had no previous experience witht the sign editor, so I read the MandelSoft's tutorial like 5 times and then I knew how to use it.

Thank you both, I've updated the guide on the official forum.

Y'all do realize that SW images will almost always be outdated because there's a time period where the old markings can still be used if the sign was there before the changes were made? But all new signs have to follow the current documents. As of right now, all new IS16a signs have to be red as see...

In the Editor under Settings (I think) change the time scale to your values. Hit OK, save and reload the map.