Yes, because QRZ? (with the question mark) means; "Who is calling me?" I'm not sure I'd call it syntax - its simply the assigned meaning, most of the Q codes without a ? question mark are a statement. With the question mark they turn it into a question. So you knew someone was calling you (you heard him sending your c/s), but you didn't know who it was that was calling you. I've not heard QRZ on its own used by Hams but I did hear a few times on Ship/Shore stuff when for example one ship( eg gbtt for example) was calling a shore station (eg gxo ) and you were in comms with the shore station he was calling, so you send ' gxo de gkyu qrz gbtt k, hoping that gxo would stop making a tea and listen to his radio (lol).