Well, I will not ever recommend that you place the antenna inside your car. None of the XM or Sirius antenna are designed to put in a car. The antennas are designed to use the metal roof or trunk of your car as a metal ground plane to pick up, and amplify terrestrial repeater signals better. Not placing it on a metal surface will lower the signal strength of the repeater signals significantly. Not only can it impair terrestrial reception, but by not providing a 360 degree view for the antenna to pick up satellite signals, can increase dropouts because you, or your car could be blocking out satellite signals depending on the direction your travelling.
I really wouldn't worry about someone stealing your antenna.
The adhesive used on roof mount antennas seals very tightly, you can just pull and it comes off easy.. It takes a several minute process to remove one! And even if they did get it off, it won't do them any good. If you cut the coax on them, good luck getting them attached to something else. The machine to put connectors on the cable costs hundreds of dollars!
Far too much work for a $39 antenna.