There is a squawk button, but all pilots I know and all air traffic controllers I know refer to it as the "ident" button since pressing the button lights up your blip on the controllers' radar screen. I had to use it once when I was doing my first long cross-country flight from Manchester, NH to Bangor, ME and got lost in northern Maine (once you leave the Portland area there's nothing to navigate by but lakes if you screw up your navigation planning, and there are a ton of them in northern Maine). The Bangor tower asked me to "ident". I did and they were able to vector me in to airport from where I was.