Originally Hill and Renko were supposed to die in the shooting in the drug house in the first episode. When it was decided that the series needed more uniformed cops to justify its title, several finished or in-production episodes were re-worked to show that both had survived and to bring them back. Other uniforms' parts were expanded as well.
Sergeant Stan Jablonski:
Let's do it to them before they do it to us.
During the opening credits when the police cars pull out of the garage, one of them has the overhead light bar on backwards. You can see that the others have the siren speakers between the lights facing front, while one has it facing to the trunk.
After the credits it shows the MTM kitten wearing a policeman's hat to match this show.