Racing game side walls

I am currently making a little racing game in Unity. I’ve designed a track in Blender and successfully imported it in Unity. My question concerns the side walls:

If you look at current formula e games like Real Racing, there are commercials all along the side walls (e.g. DHL, Visa, …). I want to randomly distribute different commercials along the racing track. I guess this should be done in Unity and not in Blender.

Are there any common/best practices for doing this?

first create an advertisement board in blender. then create all your commercials as texture and save them as separate materials,
then you can create an array of materials and swap out them in real-time randomly.