From what I understand, they are fairly common on new installations today, but weren't awhile ago. If there is a part number on the meter, or maybe it will say, that would tell you. You could also call the local water company.
If there is one, and it could be external to the meter, then you should have an expansion tank. It would be fairly obvious if you ran a little test. Buy a gauge, with the WH off (i.e., not running - the water hot), check the pressure with no valves open. Then, take a shower, bath, or wash dishes, or clothes with hot water - the more used, the better for the test. Close all of the valves so no water is being used and watch the gauge as the water is reheated. If the pressure rises, your system is closed. If it doesn't, it isn't or you have an expansion tank or some other complient hose or something that is expanding to allow for that increased volume.