CHICAGO (CBS) — After any mass shooting or terror attack, authorities always urge the public to speak up and report suspicious activity.

But what does “If you see something, say something” really mean?

CBS 2 Investigator Dave Savini spoke with the head of Cook County’s Department of Homeland Security to get some answers.

“I think the key for us to prevent these kind of attacks is to always be on the alert,” says Ernest Brown, the county’s homeland security chief. “Vigilance is gonna be the key.”

Since Brown took office last October, there have been terrorist attacks in Paris, San Bernadino, Calif., and now Orlando.

He says preventing attacks begins with the public reporting suspicious activities.

“If you see someone pacing off distances between buildings, if you see someone taking photos of HVAC systems, heating systems and security systems, if somebody is talking at work about they hate a particular group or how they sympathize with another or group or how they’d really like to do something because America is on the wrong path,” Brown said.

And he says pay attention to how someone might talk about supporting Islamic State.

“Those are at least symbolic of thought process that may lead to radicalization,” Brown said.

Also, be mindful if somebody who rarely gets packages in the mail starts taking frequent deliveries.

Brown says that if you see something, call the county hotline number: 1 855-RPRT-2-S4