The phrase "ignition button" refers to a button or switch that starts or activates something, typically a machine or vehicle. It is used to start the engine or power up the device. Full definition
This model is push - start, thanks to an electronic ignition button. (geekwrapped.com)
Upon entering the vehicle, a pulsating red ignition button beckons to be pushed. (kbb.com)
I entered the car, pushed the Ferrari - like ignition button on the steering wheel, then I started looking around for the parking sensors deactivation button; the ones in the front of the car just wouldn't quit screaming at me for no apparent reason. (drivemag.com)