Good question...
FWIW every single airline on flightradar is squawking, all the time. That's a four digit code, sent out by a box on the aircraft....the identifier allows ATC to identify in crude terms which blip on their screens is which. Sadly basic flight radar doesn't let you see those squawks. For example according to one of the other tracking apps UAE 4, which is over Kent at the moment is, squawking 4647....
For some reason "it's squawking" or similar seems to have become shorthand in some circles for the urgency/emergency code of 7700, which is a specific code entered into the appropriate box onboard the aircraft to help highlight an aircraft on ATC's screens.