Bronami

Hello, I am new to the forums but I have spent some time learning the basics of Cities: Skylines modding. I wish to edit the textures of these small billboards that appear on buildings around the city. They are able to be placed on buildings when editing them within the Asset Editor but I do not see an obvious way of editing the textures for the billboards themselves. Are there any known ways of editing textures of assets like this? Thank you for your help and time.