From Department of Homeland Security officers to counterterrorism deputies, bomb-sniffing dogs and assault rifles, law enforcement personnel are making their presence obvious in response to the Boston Marathon tragedy.
Law enforcement agencies stress there is no known connection to Southern California but say they're not taking any chances.
Authorities have vowed to beef up security and patrols in high-profile areas where crowds of people gather in the Southland.
A Metrolink rider said she heard something very suspicious on a train headed from Lancaster to Union Station on Tuesday.
"A male, 53, made a comment to a female that there was a bomb on the train," said Burbank Police Sgt. Darin Ryburn.
The train was searched in Burbank, but no device was found. Officials say people should not be worried about raising an alarm that may turn out to be false. The man was taken into custody for an outstanding warrant -- not for making the statement.
"I am not in the 'hope for the best' business, I am in the 'plan for the worst' business," said LAPD Chief Charlie Beck. "And so I would rather people call on something that might be an issue and we find out that it's a non-issue."
Patrols are up in the busy terminals of Los Angeles International Airport.
"There are other measures that are behind the scenes that passengers won't see," said Nancy Castles, a Los Angeles World Airports spokesperson.
More uniformed officers will be present for the Long Beach Grand Prix, the L.A. Festival of Books and major sporting events.
If you use public transportation, expect deputies with AR-15s, increased patrols of bomb-sniffing dogs and spot-checks of bags.
"We'll pick a location and then we'll randomly pick a person based on a preconceived number and then we'll check them," said L.A. County Sheriff's Commander Patrick Jordan. "Our goal is to be unpredictable and visible at places that you don't expect us."
Jordan said the L.A. Threat and Interdiction team is on the job, arresting parolees in the process.
A counterterrorism specialist with LAPD says something considered suspicious would be, for example, an item that could weigh 3 or 4 pounds being placed into a trash can. Or a bag, carton or backpack that is left behind by itself.
Officials stress that even for events where there is a large police presence, someone can still sneak in a device after dogs have made a security sweep. That's all the more reason for people to report anything unusual.
"We can keep things clean and pristine for an instant in time, but as soon as the crowds descend it's impossible to replicate that over and over again," said Beck.
The LAPD reminds Angelenos that safety is a shared responsibility, and it's always smart to be alert and aware of your surroundings. If you notice anything suspicious, report it.