Stunned police had only to sit and watch, as 500,000 protesters hit the streets of L.A. in what turned out to be a perfectly peaceful march Saturday. City police said there were no incidents or arrests. The demonstration was intended to send a message to Congress that its plans for immigration reform -- which target immigrants, employers and even Samaritans -- are not well received. "I've been on the force 38 years and I've never seen a rally this big," said Cmdr. Louis Gray Jr., incident commander for the rally.