LOS ANGELES - California made history by becoming the first "sanctuary state" in the United States as a new law showing a will to resist the White House's immigration policy went into effect Monday.

The law, which was called SB (Senate Bill) 54 before being signed by Governor Jerry Brown in October, vastly limits cooperation between state and local law enforcement officers with the federal Immigration and Customs Enforcement agency.

According to the federal government's definition of the terms, sanctuary states and cities are those that do not collaborate with immigration authorities by transferring custody of undocumented immigrants who are detained at a county or city jail.

"This bill would, among other things and subject to exceptions, prohibit state and local law enforcement agencies, including school police and security departments, from using money or personnel to investigate, interrogate, detain, detect, or arrest persons for immigration enforcement purposes," it reads.

According to the law, Californian law enforcement cannot inquire about an individual's immigration status, arrest people on civil immigration warrants, or participate in border patrol activities or joint task forces with the federal government if the primary purpose is immigration enforcement.

Meanwhile, the state law enforcement can only detain someone at the request of the federal government, notifying the latter to release or transfer someone to federal custody, after there is a felony warrant or the person has been convicted of one of the more than 800 crimes on a list attached with the law.

The law, dubbed by US Attorney General Jeff Sessions as "unconscionable", triggered a national debate over how far states and cities can go to prevent their officers from enforcing federal immigration laws.

"The bill risks the safety of good law enforcement officers and the safety of the neighborhoods that need their protection the most," Sessions said in September before the law was signed.

But Brown fired back immediately, strongly defending the measure as a "well-balanced bill" and a reaction to "this kind of xenophobia we see coming out of Washington".

"It protects public safety, but it also protects hardworking people who contribute a lot to California," Brown said.

Drivers heading to California had seen fake signs decrying a new immigration policy on at least two highways, welcoming them to an "official sanctuary state" that's home to "felons" and gang members.

State officials removed a sign on Tuesday on the Arizona line and another on Monday near the Nevada border, Department of Transportation spokesman Mark Dinger said.

The fake signs appeared just under the official "Welcome to California" markers and referenced the Central American street gang MS-13: "Felons, illegals and MS13 welcome! Democrats need the votes!"

Xinhua - AP