I want to use the following BNC connector on the PCB I am designing: https://www.mouser.ca/ProductDetail/Amphenol-RF/031-5493-1010?qs=py4qCovljJ%2FMGk8N0v0eQw%3D%3D
The pin physically in the center (2) is the signal pin (center of the BNC). The other pin is Ground.
The MH snap-in pins are for 2mm diameter mounting holes, they are electrically isolated from the rest of the connector in this particular model so you can leave them floating or ground them as you prefer.
That symbol is really terrible, and should be improved to at least show which pin is which, lest an expensive error occur.