Also, to sign-up via CWOP/APRS-WX feeds you must be a licensed amateur radio operator and use your callsign. Otherwise, I don't think you can feed your wx data to them using the APRS feed. Again, I may be wrong but that is how I understand it. Privacy of your personal name is lost when you do this...
A callsign isn't required, unless one want's to be able to send weather reports through the APRS servers.
Some may not understand the difference... Up until a few years ago, all CWOP weather reports went through the APRS servers, but the load of ~8000 CWOP stations connecting exactly every 5 minutes was causing problems for the APRS servers. Since then, dedicated CWOP servers have been put in place and most CWOP weather reports now go through those. Those with a callsign, can obtain a password to enable them to send reports through the real APRS servers. FindU collects reports from both the APRS and CWOP servers, and then MADIS collects the data from FindU, so it really doesn't matter which the reports go to.
To expand upon the "Privacy is lost..." part, the name and address of people with a HAM callsign is public record.
