This is a basic template for making your own billboard in payday 2

Make sure you have software to edit the .DDS images i recormend paint.net

how to edit the .DDS image
step: 0: make sure to extract the .zip file in your mod_overrides folder
step 1: open the .dds file in gimp or paintnet
step 2: put the image you want to use on the pink area
step 3: save the image as a .DDS image in the same folder (Make sure to overide the prexitsing .DDS file)
step 4: change the file type to .texture by renameing it (make sure in windows in the view tab of file explorer the "File name extensions" box is ticked)
step 5: launch PAYDAY 2 with this mod in the mod overides folder under the assets folder
step 6: enjoy the mod or publish it on modworkshop and also make sure to delete the .txt file in the main folder

Paint.net download link: https://www.dotpdn.com/downloads/pdn.html

if you have problems looking for the template this is the file path:
Billborad template\units\payday2\props\str_prop_street_sign_roof