Some kind of security fasteners on its mountings. Like the bolts where the hex snaps off when tightened or Allen key fixings and drill out the hex. Will have to be removed with a disc at the end of life, but not a problem for normal maintenance.
Can’t belive someone would bother stealing a used exterior unit, the resale value on the black market must be a pittance.
Steel cages installed over the top of your unit prevent unauthorized access. The cage can be fastened to the slab, preventing whole unit theft. And their mesh walls prevent hands from reaching into the unit for the copper coils they are ultimately after.
I guess they just pinch them for the scrap metal value 🙁