From the Department of Homeland Security:

Across the country, in our communities, we share everyday moments with our neighbors, family, coworkers, and friends. We go to work or school, the grocery store, or the gas station. It's easy to overlook these routine moments, but as you're going about your day, if you see something that doesn't seem quite right, say something. By being alert and reporting suspicious activity to your local law enforcement, you can protect your family, neighbors, and community.