I had a 97 TJ with something similar to that installed on it, about the same spot but above my left knee. It was in fact an anti-theft device. It was installed at the Jeep dealership (I'm guessing to help prevent vehicles from being stolen from the lot given the neighborhood it was in) and they would try to upsell you on keeping it and/or use it as a negotiating point when you purchased a new vehicle from them. They would also remove it at your request upon purchasing the vehicle. I bought my '99 Cherokee from the same place, but they had traded another dealership for it and never bothered to install one since I picked it up the day they took it into inventory.
