1: Install this mod:
https://www.gta5-mods.com/vehicles/mtl-tanker-add-on-template-ag_mods
2: Extract the "tanker_sign_6.dds" and "tanker_sign_7.dds" files
3: Add them to the "mtanker2.ytd" and "mtanker2+hi.ytd" files in "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\update\x64\dlcpacks\mtanker2\dlc.rpf\x64\vehicles.rpf\"