While talking to someone way smarter than me we collaboratively determined that FCC issued Amateur Callsigns constitute PII.
For the following reasons:
PII is defined “Any representation of information that permits the identity of an individual to whom the information applies to be reasonably inferred by either direct or indirect means.” US Department of Labor 1
FCC Callsigns are issued by a federal agency specifically as a unique identifier that is inextricably linked to an individual with the sole purpose of identifying the individual. US FCC 2
When getting a callsign from the FCC, by registration and license requirements, you are required to give your name and address for publication broadly. If the callsign is searched on the ULS, that information is all publicly accessible.
In essence, this isn’t too much different from the government suddenly deciding to publish all License Plate numbers to a public database, or social security numbers to a public database. This information is often used for advertising purposes (ARRL is a big one here), correspondance between Radio Amateurs (HAMS) often in the form of QSL cards, and, in some cases, to abuse and harrass radio amateurs 3 (citation as one example only, with an interesting discussion in the thread).
Ultimately, there is a case to be made whereby we have to push our senators and representatives (such as they are) to have the FCC remove these addresses and PII from a publicly accessible database. An easy solution would be to include a method for digital communication of the station (an obfuscated email address for instance) and removal of specific address of the station, leaving only general location. This tracks also with the fact that when transmitting required location, that is provided not in address, but grid reference. Which is more reliably than address for a mobile ham (which many are at least part of the time ).
Just my two cents on the issue, but something I think should be considered moving forward.