The Hill Street Precinct E.A.T. van, which is also used as the van that the Polk Ave. Precinct used to drop the homeless off on the Hill, is number 2227. There is also a squad car with the same number. The same with 2225, which is used on a larger newer E.A.T. van as well as the number for a squad car. Each number should have only been used one time.
Many of the street cops are seen wearing scarfs during the colder seasons. No street cop would ever wear a scarf as part of his uniform, as a suspect or perp could possibly use it to strangle the officer if they got into an altercation.
When the various characters speak into the radio microphone in their patrol cars, they seldom press the "transmit" switch, and Andy Renko is occasionally seen speaking into the back of the microphone.
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.
Although the city the show takes place in has never been revealed, it's been said to be based either on Chicago or Philadelphia. That being said, in many background shots the very distinctive Los Angeles City Hall tower can often be seen. The show's exteriors were filmed in older sections of Los Angeles near downtown.
The department is part's of a large city's police force, presumably with hundreds, if not thousands, of officers. However, most (all?) of the badges seen worn by officers have predominantly two-digit and occasionally three-digit numbers.