I made a bunch of signs in a red and white theme for my new map "Iris by   Zhuckar. They are very minimalistic, some are just completely red or white so you can use your signs as lamps.
To make them work just trasnfer them to the Trackmania\Skins\Any folder and they should merge with the existing folder. Locaters are included so the signs will work online.

Download here:
https://drive.google.com/drive/folders/1fakueKoGOTCT430MfUvlD49hWL5uAsMw?usp=sharing

If you want to see an example of how custom signs can change the look of a map check out this video:



Enjoy!