If single phase you'll notice sometimes it has a little extra ground wire connected (now mostly obsolete), for 3 phase it doesn't, in both cases it will say so on the outside (typically: the test current, and usually there is a test button which makes them easy to identify, this test button forces a small leak causing the circuit to become unbalanced resulting in a trip (if it doesn't trip when the test button is pressed the breaker is considered faulty and should be replaced).
For instance, here is an 'Eaton' 3 phase breaker with integrated ground fault protection circuitry:
Note the little yellow 'test' button. That's a 30 mA fault current device, you can have higher permissible fault currents for certain gear that tends to be a bit more leaky which would otherwise cause nuisance trips. These little things are quite the work of art inside, if you ever have a faulty one I would encourage you to pick it apart to see what makes it tick.
For instance, here is an 'Eaton' 3 phase breaker with integrated ground fault protection circuitry:
https://www.omnical.co/products/eaton/1742431/2259595
Note the little yellow 'test' button. That's a 30 mA fault current device, you can have higher permissible fault currents for certain gear that tends to be a bit more leaky which would otherwise cause nuisance trips. These little things are quite the work of art inside, if you ever have a faulty one I would encourage you to pick it apart to see what makes it tick.