San Francisco police have stepped up security around the city in the wake of the Berlin attack that killed 12 people and injured dozens more at a Christmas market.
Police say the intent is to increase presence, not fear. They say these situations are unpredictable.
"Sometimes terrorism is a random act," said Giselle Talkoff, spokeswoman for the San Francisco Police Department. "Sometimes it's not a group planning it or an individual planning it by themselves. So you might not know when it's going to strike."
Police presence was increased at several tourists spots around the city, including Union Square.
The Woschnagg family of Frankfurt, Germany, was among the thousands of holiday visitors to downtown area. Before they left home, the Woschnaggs saw how police were reacting to the Berlin attack.
"They had policemen running around, standing there with machine guns, which is unusual," Karl Woschnagg said. "That hasn't been the case before in Germany."
Woschnagg said the increased security around San Francisco "feels comforting."
Workers from Cathay Pacific Airways also appreciate the heightened presence and police discretion.
"Definitely, it's something that needs to be done for the safety of everybody," Jorge Gordillo of San Francisco said. "Very sad. But it is what it is, and we're in a different world nowadays."
Simren Khurana of Danville said it really has an effect on everybody: "Because anybody could be in that situation. And that's something scary."
Officers said they do not want to impact the holiday spirit but they also hope visitors will alert them to anything suspicious or needing attention.