I agree that security TORX® fasteners will give some measure of theft deterrence. Nothing will stop a truly determined thief, but make it difficult or time-consuming enough and they will seek out easier pickings. These guys
http://tamper-pruf-screws.com/ have a large assortment of fasteners and tools. If you want to take deterrence (and cost) to another level there are specialized theft-deterrent fastener systems like Pitlock
https://www.pitlock.de/en