First the crook picks a location. A busy shopping mall is not a good place. A deserted parking outside town with lots of escape routes is. When on a big parking try to park the car on the side. A thief is still protected by cars on either side of your vehicle so try to make at least one side visible to the public. Pick a path were many people walk by, for example to the exit.
Cars a picked by price and model. If you have a BMW you certainly have money for a good stereo. If you have a Lada you probably also have a budget radio. If you drive an average car but it has light alloy wheels, extra spoilers, a shiny exhaust or even worse stickers with the make of your audio system you are an excellent target. Small average looking cheap cars are not even looked at. If you have small car but it is filled with expensive audio equipment, try parking the car next to some more expensive cars to distract the burglar.
After the thief took a look at the possible targets he/she will take a look inside the cars. Here's were your stock lookalike audio system comes in handy. If your audio system is totally invisible, don't use a flashing red light either. Why would this car have an alarm, there's nothing there or is there? If your car seems like a potential victim on the parking lot do use a flashing red light showing you have an alarm. This makes your car less attractive than cars that don't have an alarm.
Professional burglars know what they are doing. They see they difference between a fake alarm and a real one. They also know that big subwoofers in the rear of your car mean that there's got to be an amplifier in the car somewhere. Most of them can even tell the exact make and model of your head unit by the part that's still left after removing the detachable face plate. Less experienced crooks break in once or twice because they need the money or because the see an easy target. They don't know the difference between a Pine and Alpine unit. Statistics show that detachable face plates are the safest option. Number two is the removable unit followed closely by the key card system from Blaupunkt. As many people hide the detachable face plate in the glove compartment or the entire head unit in the boot, cars will still get broken into. If possible leave the glove compartment open when parking so everyone can see there's nothing there.