The easiest way to tell is that the air conditioning system uses a different refrigerant. With the heat pump, it uses R-744 - pure carbon dioxide. The cars without the heat pump use R-1234yf. Under the bonnet there's a label listing the AC refrigerant and its global warming potential CO2 equivalent ratio. Unsurprisingly, R-744 has a GWP of 1.0.
My ID.3 has a heat pump but it's hard to know what impact it has. In cold weather, the car uses a lot of energy to warm up the battery and you typically have more rolling and air resistance. I also fit winter tyres, so a comparison is even harder.
My understanding is that it makes a difference mostly on long journeys, as the HP is much slower to produce heat than the normal resistive heater. It's also using waste heat from the battery and drive system as a source as well as the outside air.
There are some technical diagrams of the difference between the two systems here:
https://www.id4manual.com/heating-air-c ... -pump.html
https://www.id4manual.com/heating-air-c ... -pump.html
