In the early-morning twilight on a cool Friday in April, a half dozen people gathered in a small parking lot in the San Diego neighborhood of City Heights. It was quiet, before the working-class neighborhood had come to life with the bustle of traffic, commuters, and the sounds of children walking to school.

One of the men there, Benjamin Prado, grabbed a bullhorn and a radio. “You all have your walkies, right?” he asked the others as he got into a car. Its rear bumper had a decal reading in bold Spanish, ‘Patrullas Comunitarias’ or ‘Community Patrol’. The group nodded. They agreed to meet back up later that morning before dispersing in several cars that disappeared in the predawn darkness to carry out their mission of patrolling the neighborhood in search of suspicious vehicles and activity.

Prado and his team aren’t law enforcement, private security, or even neighborhood watch, but members of Unión del Barrio (UdB), an independent Chicano political organization. The group is working to warn the surrounding San Diego community of potential U.S. Immigration and Customs Enforcement (ICE) activity in the area, offering a first line of defense for families at risk of President Trump’s plan to enact mass deportations throughout the country.

During the Friday patrol, Prado drove slowly down quiet neighborhood streets lined with small homes and apartment complexes. UdB’s community patrol members are specifically trained to look out for signs of undercover law enforcement vehicles—usually U.S.-manufactured vehicles such as Dodge Durangos, Ford Explorers, and Chevy Impalas with dark-tinted windows that stand out from others in the neighborhood. Trucks and SUVs with no license plates and with lights on the grill and visor are other hallmarks that volunteers look out for.