I've seen you've put the taxi sign of the hovercar on your mod in photoshop, feel free to actually take it, it should work plug and play when copied over from the hovercar.
Bit confused by what you said, from what I know is that i can use your taxi sign whihc i cant currently find.
Ok, since Bernd gave you the permission to use his taxi sign, the whole process is way easier. Thank you @Bernd! First of all you have to extract the taxi sign from his mesh. Download his mod, load the burnside.dae in any 3d application (like Blender) get rid of all the unnecessary meshes and export the file. It's the flexbody 'taxisign' which is linked to the burnside_police.jbeam. Additionally you have to copy the materials Bernd created for the sign. Have a look at his materials.cs file and search for the taxi sign material as well as the 'black' material. Last but not least add the 'burnside_taxisign' to your pc file.