How do you figure out which side of a car the fuel tank is on?

I have this problem when driving my wife’s car: Why Do Cars Have Fuel Doors on Different Sides

But here’s the kicker. Commenter spewlman advised:

Want to avoid the frustration of not knowing what side your gas tank is on? Car manufacturers actually solve this mystery for you. On your dash is a picture of a fuel pump. The pump will either have the hose/pump on the side that your tank is on, or will have an arrow pointing to the side your tank is on, or both. Never wonder again – just look at your dash, regardless of what car you are driving.

I have managed in the past by staring at the side mirror down the body of the car, looking for a slight perturbation of the fuel door. If this trick with the dashboard works, I guess I won’t have to do it any more.