Hold down the home button until Siri comes up. Say "who am I?". Look at the results and do the right thing: call your local PD's non-emergency line and report

Hold down the home button until Siri comes up. Say "who am I?". Look at the results and do the right thing: call your local PD's non-emergency line and report it as found property. Give them the info you found. They can figure out the rest. If it's not a 4S, skip the first part, then call it in anyway.