After years of failed attempts, California has become the tenth U.S. state that will allow unauthorized immigrants to apply for driver's licenses.

MAP: Status of undocumented immigrant driver's license laws nationwide

Governor Jerry Brown signed a landmark bill Thursday morning at Los Angeles City Hall, which will allow people who are living in the U.S.illegally to obtain a California driver's license. But there's still much to be determined before the measure kicks in by January 2015, as planned.

Between now and then, the California Department of Motor Vehicles must complete two major tasks: Collect input on what the licenses will look like, and determine which documents can be used for identification by a pool of applicants who don't have Social Security numbers. 

"They are going to have to take input on what documents are acceptable, but also on what changes are going to  be minimally necessary in order to comply with the Federal Real ID Act," said Democratic Assemblyman Luis Alejo of Salinas, who sponsored the driver's license bill, AB 60. "That federal law requires states who are granting these types of driver's licenses to have some distinguishable letters on the license."

The look of the new licenses – in particular, how obviously they'll identify someone's immigration status – was a major point of contention for immigrant advocates. While there's no prototype yet, Alejo said the difference between these and regular California licenses will be minimal.

For example, he said, the front of the licenses would read "DP" for "driving privilege" before the license number, instead of the "DL" seen on regular licenses. There would also be language added to the back of the licenses stating limitations, such as that the holder may not use it for federal purposes, like using it as identification to board an airplane.

As proposed in the bill, applicants who lack a social security number would be able to present their birth certificate, a consular identification card, and proof of residency in California. Alejo said other documents will likely be included in the DMV's regulations, such as foreign passports and school records.

More than a million applicants are anticipated to apply in the first year, which Alejo says also means the DMV will consider adding staff and offices to handle the logistics. Alejo said there's a chance the program could kick off next fall if the state wraps up the preliminary work sooner.

This will be the first time in decades that unauthorized immigrants in California can obtain driver's licenses. In 1993, a measure signed into law by Republican Gov. Pete Wilson required driver's license applicants to provide a Social Security number and proof that their presence in the state was "authorized under federal law."

This essentially blocked people without legal immigration status from obtaining California licenses. Soon after, former state Assemblyman and current Los Angeles City Council member Gil Cedillo began proposing bills to restore their access. One was signed by Democratic Gov. Gray Davis in 2003, but Republican Arnold Schwarzenegger repealed it after Davis was recalled. Schwarzenegger later vetoed another Cedillo license bill.

Cedillo's subsequent attempt didn't get very far until last year, when Brown signed a bill Cedillo sponsored ensuring that young immigrants who win temporary legal status under deferred action may obtain licenses. The law kicked in last Jan. 1, but was viewed by some critics as a token since it covers relatively few people.

AB 60 will allow a much larger number of unauthorized immigrants to drive legally in California. The state is home to nearly two-and-a-half million people who lack legal immigration status, according to one recent estimate. But like other drivers, these license applicants will need to pass driving tests, and must obtain auto insurance.

Alejo picked up the proposal after Cedillo hit his term limit last year; both plan to join the governor at the City Hall signing ceremony.

Unauthorized immigrants are allowed driving privileges in nine other states, along with the District of Columbia and Puerto Rico.