Catalytic converters are filters that are connected to your vehicle's exhaust system to reduce the amount of harmful emissions. Every gas engine car in the United States of America is required to have an adequate catalytic converter on its exhaust system. The catalytic converter is connected to the exhaust pipes that are coming from the headers. Then it is connected by another exhaust pipe to the muffler, where the exhaust gases are released.
Look at the exhaust fumes coming out of the muffler. When a catalytic converter is not installed, you will see medium to dark smoke coming out of your muffler. Also, the smell of the burned gasoline will be considerably more potent in a car without a catalytic converter than a car with one.
Listen to the exhaust. The catalytic converter helps reduce the sound in a car, just like the muffler. A car without a catalytic converter will have a loud exhaust note.
Check the exhaust system under your car. The catalytic converter will look like a bulge somewhere in the middle of the exhaust piping in between the muffler and where the headers connect to the exhaust downpipes (see the illustration in the resources). If the bulge is not there, you do not have a catalytic converter.
