As a professional installer, every day I'm comfronted with people who faithfully remove their aftermarket stereo face but still have their stereo stolen. In the process of stealing the stereo, thieves also cause damage to the door and window and steal other items from the car.
If you still have - or can get - an original factory stereo, you can disassemble it and hollow out the face to use as a decoy. Then at least you have one less thing enticing someone to break in. This works really well on the 92-95 Civic because it has a deep recessed opening to support the false faceplate. Other cars will need more creative methods of attaching it.
Here's your aftermarket stereo enticing bastard thieves to break into your car. If there's a nice stereo, there's probably some other nice equipment in the car too.
From the front there is no indication that the radio has been hollowed out. The circuitry behind the screen is now gone, but the bare aftermarket stereo behind it makes it look natural. All the buttons and knobs are fixed in place.
Everything inside the face that was not visible from the front was removed and then hot glue was used to hold the buttons in place. ABS plastic was glued over the holes left by the cavities around the knobs. Then the knobs were glued on top. The height of the false faceplate was cut in half.
This is the end result. Remove your aftermarket faceplate (but leave the trim ring) and rest the false oem faceplate on top. This may be enough to cause a thief to move on to another target.