Outside a Chinese supermarket at a popular shopping mall in Milpitas, California, a volunteer came up to every shopper, reminding them to leave nothing of value in their vehicles.

The mall, close to two freeways, has experienced an increase in car break-ins this year. Local authorities have partnered with the retail center by posting signs in the parking lot and cautioning shoppers about leaving belongings in their cars.

In Silicon Valley, one of the wealthiest regions in the US, residents have been increasingly frustrated with "smash-and-grabs" — in which a car's window is broken and valuables inside stolen.

Photos of vehicles with signs indicating the car is unlocked and there is nothing to steal circulate on social media in attempts to deter thefts.

In the Twitter account "SF Car Break-ins", people post photos of their smashed vehicles and others' daily. Lost property includes cellphones, laptops, jewelry, projects they were working on, and items of sentimental value.

"Since a year and a half ago, we have noticed the spike (in auto burglaries)," Captain Sean Washington of the Fremont Police Department told China Daily. "Over the last year, there's been a tremendous increase in the Valley, as you can tell. All the jurisdictions are experiencing that same increase."

San Jose, the largest city in Silicon Valley, reported 6,721 cases in 2018, a 14 percent increase from 2015, according to data provided by the office of California Assembly Member Kansen Chu, who successfully pushed recently for $3.75 million in state funding for several Silicon Valley cities to address the problem.

The city of Santa Clara saw 125 percent car break-in increase the first three months of 2019 compared with the same period a year ago.

The Newark Police Department projected a 93 percent increase this year due to the high number of incidents from January to February.

Police generally blame the vibrant economy and criminals taking advantage of the situation for the spike in the smash-and-grab crimes.

"It's a combination of community members leaving items of value in their cars as a crime opportunity, and the profit that these individuals are able to achieve by grabbing property and then reselling it on the black market. All of that has led to the spike," Washington said.

"More people have cellphones and laptops now. It's more commonplace. Go backwards 10 years from now, there were not so many cellphones to steal," he said.

The Fremont Police Department recently intercepted a container full of more than 1,000 laptops headed overseas, and the container was filled in just one weekend of criminal activity.

The shopping centers that get hit the hardest are those near expressways and freeways because it's convenient for suspects to flee those areas, and it's usually more difficult to investigate, said Washington.

Police also have found that freeways have become a more common venue for gun violence in the San Francisco Bay Area. There were 189 freeway shootings in the region between November 2015 — when the California Highway Patrol began keeping track — and April 2019, according to a report by The Guardian last month.

The number of freeway shootings has increased on nearly every major highway in the region, such as the north-south Route 101 corridor linking San Francisco and Silicon Valley and the Interstate 880 corridor connecting Alameda County to Silicon Valley.

Though elected officials and law enforcement could not determine the root cause for the rise of car break-ins and freeway shootings, Mary Knox, deputy district attorney for Contra Costa County, points to the displacement of longtime residents from cities, where the average cost of rent has exceeded many working-class families' budgets.

Gun violence has become "more transitory and regional" in recent years, much like the lives of people who have been displaced from the Bay Area's gentrifying urban core to far-flung suburbs and now rely on highways to get around, Knox told The Guardian.

In Silicon Valley, home to the headquarters of some of the world's most valuable public companies, chiefly in technology, more residents are now struggling to afford the growing costs of living as home prices continue to skyrocket.

Median home prices in Silicon Valley increased by 21 percent to $1.18 million in 2018; the rental rates in the San Francisco and San Jose metro areas were significantly higher than in any other metro area in the nation, according to the 2019 Silicon Valley Index by Joint Venture Silicon Valley.

Fremont Vice-Mayor Raj Salwan told China Daily that the suspects involved in those cases mostly experienced a breakdown in family structure due to an increasing income gap, displacement and other reasons.

"I haven't studied it, but it's something that certainly we should be looking into," said Washington.