Setting the mood when gaming can be very important to some people. Anything that helps them 'fall into' the game while playing. So it's time to discuss some mood setters for a COPS game. Some of these are great to use every game while others not so much.
The muster room. Hill Street Blues always started off with this each episode. All the officers going on shift getting the run down on what's been going on and things they will have to deal with. I highly suggest starting off each game with this. You can then drop hints at upcoming storylines, update some of the ones which have gone stale and not to mention it gives you the ability to railroad a little bit without looking so much like railroading. Just remember be safe out there guys.
Also a nice collection of music helps as well. I used to start games with a different cop show theme song along as with playing one each time we took a break. There are plenty of others out there that fit the bill as well. Take a look around online for a few soundtracks or collected scores that are inspired by various shows like Dragnet.
Have a pot of coffee on for whoever wants some. Even for those who don't drink it the smell alone will fill the room. Go with the old police stereotype also and maybe put a box of Krispy Kremes out on the table as well. Only allow refills or seconds when the characters are at a location that would allow them to do so.
Many times I would run games where the characters were regular duty police officers. So they would be two to a car partnered up during the game. At the table I would make the players set beside each based on who they were partnered up with. The only way they were allowed to pass information to other pairs of players while on patrol was through the radio.
Whenever they grab the radio to pass along that information, get ahold of the dispatcher or call for backup they have to use the 10-codes. Don't expect them to memorize it, make a few copies and pass them around the table and don't rush them to hard. After a couple of games the commonly used codes will become second nature.
Props are pretty much limited by your budget. You can plastic badges and toy guns. Or you can purchase actual evidence kits online and fill them with all sorts of things. Examples of paperwork can also be found on the net with relative ease (just don't bury them in it as gaming is about having fun more than frustration), If you do get extravagant with the props be sure to take some pictures and send me a link!