Police Sedans can be found throughout Harran. Many are found to be already looted, but some appear to still be intact. They must be lockpicked, at a difficulty of 'Medium'. If opened, money, valuables, weapons, and rarely, Firearms can be found in their trunks. If a firearm is found in there, it is often a German/American 9mm pistol. In even rarer cases, Police Rifles can be found. Be aware though, there are often Infected wandering around there, so it can be a risk trying to lockpick them. Make sure it is clear of infected before you attempt to lockpick them. Make sure to carry at least 3-5 Lockpicks.
Police Vans are found throughout Harran, but rarer than the Police Sedan. The lockpicking difficulty is 'Very Hard', so it is recommended to carry at least 7 lockpicks with you. Like the Sedan, many infected, such as Biters and Virals can be found in it's vicinity; so you should clear it of any threats before you attempt to lockpick it. They are more likely to carry valuable loot, such as Police Rifles and pistols.