I checked the exif data on the pics from my phone. I keep the GPS off until I actually need it, and have been actively aware to check for that before I take the pics. I use xnview and it has a feature for manipulating the exif data, such as modifying, scrubbing, exporting... So I exported to see what it actually shows. There is no serial number on mine, as far as I can tell.
So then I was thinking... If I include the GPS but *change* it, perhaps to an officer's address, who I'm aware lives down the street.. Then wouldn't that be interesting to watch what happens?