On Mon, 19 Apr 2004 21:42:51 -0500, "O. Sami Saydjari"
wrote:

I believe it also provides the controller with your tail number
automatically. -Sami

Yup. If you look at the Fed's registration database:

N2057M is Assigned

Assigned/Registered Aircraft

Aircraft Description

Serial Number 28R-7803103 Type Registration
Corporation
Manufacturer Name PIPER Certificate Issue Date 02/06/2004
Model PA-28R-201T Status Valid
Type Aircraft Fixed Wing Single-Engine Type Engine Reciprocating
Pending Number Change None Dealer No
Date Change Authorized None Mode S Code 50323757
MFR Year 1977 Fractional Owner NO

The mode S code is hard-wired into your transponder and tells big
brother who you are.

They also have a provision for pilot-programmable "flight" number.

Other biggie is for TCAS resolution advisory capability, the xpdr's
talk to each other to ensure a compatible resolution (as in plane A
climb, plane B descend).

TC