[aprssig] US APRS symbol usage

[Bill Vodall WA7NWP]

> I was surprised at that also, but then again, homes are easier/cheaper
> to set up.  Remember, this is from APRS-IS, not RF.  Therefore it counts
> all of those Internet-Only UI-View, xastir, and other APRS-IS clients
> that "beacon" to the Internet.

It's easy, and a good thing, to exclude the TCP path packets from the
APRS-IS feed...

Bill - WA7NWP