Securing the Cities Improvement Act This bill makes changes to the Securing the Cities program. Specifically, the bill requires the Department of Homeland Security (DHS) to establish performance metrics and milestones for the program. In carrying out the program, DHS must designate jurisdictions based on the capability and capacity of the jurisdiction relating to preparedness and response, as well as the relative threat to, vulnerability of, and consequences for, such jurisdiction regarding terrorist attacks and other high-consequence events utilizing nuclear or other radiological materials. DHS must report to Congress within two years regarding participation in the program, the establishment of metrics and milestones, performance against such metrics and milestones, and plans for any changes to the program.