S-COMM is a US program somewhat similar to the state's program in Arizona: S.B.1070.
S-COMM cities must send the fingerprints of all persons arrested to ICE - the US immigration agency. That's "all persons" -- even those arrested for a minor offense, such as sitting on the sidewalk. And those later found innocent after trial? Tough! ICE got your fingerprints months before.
ICE says S-COMM is optional for cities. SF Sheriff Mike Hennessey and the Board of Supervisors requested the exemption for San Francisco. Atty.General Jerry Brown has so far refused to grant it.
These speakers at the July 29, 2010, rally at Brown's office in the State Building at 455 Golden Gate, give more details:
More on S-COMM, and here's the SF Sanctuary City Ordinance. Reminder: S-COMM is a federal government program from which Atty. Gen'l. Jerry Brown has the power to exempt California cities; and a Sanctuary City program is a local government setting policy for its police department.