As the Christmas shopping season lights up, police throughout Sonoma County are reminding merchants and consumers to stay alert for thieves, scams and overall personal safety during these hectic weeks.

In Petaluma, downtown merchants share photos of known scammers, people who have used fake or stolen credit cards before.

Santa Rosa police and a team of volunteers keep a lookout for lost or confused shoppers downtown, or those who leave packages in view in their cars in mall parking garages.

"Thefts and shoplifting are more common this time of year," said Petaluma Lt. Tim Lyons. "We see a rise in property crimes in general during the holiday, with people leaving Christmas gifts in their cars or forgetting to take things in at night."

Volunteer police "ambassadors" walk Santa Rosa downtown streets, welcoming visitors, giving directions or assisting shoppers, said Sgt. Andy Romero.

The teams of two, including David Cooper and Dave Lichtenstern,greet residents and visitors, acting as liaisons between merchants and downtown users.

"We want people to feel safe and welcome," Romero said. "They may help people with directions or hours or help point out where things are. They're kind of a walking concierge."

But they also serve as another set of eyes and ears for anything suspicions or nefarious happening downtown as shoppers hustle from one store to another, sometimes allowing their vigilance to drift away like yesterday's tinsel.

"If they see something odd, they would call dispatch," Romero said. "They may pop into a merchant's and someone may say, 'By the way, we had this bad check passed.'"

In Petaluma, communication with downtown merchants led to the arrest of Jennifer Weissenberger, 40, of Petaluma, who is suspected of at least six theftss since Nov. 24, according to police records. Police and merchants say she used fraudulent credit cards and lies to obtain services and goods from several stores.

Sgt. Brad Conners, in charge of the downtown Santa Rosa police patrol, said no major shopping-related crimes have been reported this season — like skimming, when someone steals a personal identification number for a bank or credit card and makes unauthorized charges.

More common is when shoppers, perhaps overwhelmed by deep discounts, twinkling lights or too much eggnog, leave packages in view in their vehicles.

"Everybody's in a hurry," Conners said. "Every year, we get burglary reports of people who are out shopping and they leave their recent purchases in their cars, and people break into their cars and steal them.

"It's easy pickings when they're visible."

Most thieves are lazy, he said, urging people to lock their car doors: "If you leave items in plain view, people won't hesitate to break in."

Even the appearance of value is enough temptation. Police warn not to leave backpacks or briefcases in vehicles, because thieves will break a window to get to where they think a laptop might be — even if the backpack contains only textbooks.

In addition to advising shoppers to keep track of their surroundings, merchants are urged to protect themselves from dishonest shoppers.

In Petaluma, Lyons said merchants have been struck by thieves using fake or stolen credit cards. Merchants who ask for a photo ID and compare the names and signatures can often prevent fraud before it happens.

Petaluma also has officers on downtown foot patrols through Christmas.

Police also advise storing receipts in a safe place. Thieves have been known to collect discarded receipts, then try to fraudulently return a new item as if they'd purchased it, walking away with cash.

(You can reach Staff Writer Lori A. Carter at 762-7297 or lori.carter@pressdemocrat.com.)