The number they’d need for gasoline is 1203, one of the few i have memorized. If you ever see a number on a truck, you can look it up on a hazmat number lookup site and it’ll tell you what it’s hauling. Usually it’s gas, diesel, or propane, but sometimes it’s something more fun

Edit: i saw a truck with the number 1824 on it, looked it up, and it’s a Sodium Hydroxide solution