Polarity of Ultrasonic Sensor
As people have already indicated in the comments, from the perspective of the actual ultrasound signal (transmitted and/or received) it doesn't make any difference at all. But my intuition tells me -- and small features in the drawing seem to indicate -- that one of these terminals is probably tied to the outer shield.

Without an actual part number and/or datasheet we have no way to be certain. But what we know for sure is that this part has a shield, and the shield needs to be connected to something to be useful. If this is a 2-pin device, then yes it's a safe bet that one of these terminals is connected to shield and the other isn't, so yes polarity matters.