The signs, which can be seen by motorists entering California from Arizona and Nevada on Highway 95, say, "Official Sanctuary State: Felons, Illegals and MS13 Welcome! Democrats need the votes!"
California became a sanctuary state on Monday as a bill signed in October 2017 by Governor Jerry Brown officially took effect. The legislation "vastly limits" who local and state law enforcement agencies in California "can hold, question and transfer at the request of federal immigration authorities," the LA Times reported.
"These are uncertain times for undocumented Californians and their families, and this bill strikes a balance that will protect public safety, while bringing a measure of comfort to those families who are now living in fear every day," the 79-year-old Democrat said.
But this is not the first time that the state has seen such signs. In April 2017, a similar billboard mocking Malibu's decision to become a sanctuary city caught the eye of drivers.
"Official Sanctuary City: Cheap Nannies and Gardeners Make Malibu Great! (Boyle Heights Not So Much)," it read. The April sign was later taken down by officials.
It is unclear who posted either signs.
Following the announcement that California would soon become a sanctuary state, several members of the Trump administration spoke out against the move.
"The bill risks the safety of good law enforcement officers and the safety of the neighborhoods that need their protection the most," Attorney General Jeff Sessions told the Times.
Thomas Homan, acting director of ICE, also criticized Brown's decision, calling it an attempt to "codify a dangerous policy that deliberately obstructs our country's immigration laws and shelters serious criminal alien offenders."
However, immigration rights activists called the move a "victory" that will help keep thousands of families together.