How can you tell which fuel a gas cooktop is set...

Question

In one of your answers you stated that the person needed to make sure the cooktop was set up for the right fuel (lp/nat gas)

How do you do this by looking at the unit?

I have low flames for the btu ratings of the unit and the burners seem like they are starved for gas. I have natural gas supply that has been checked for blockage although not for pressure.