Among Marriotts, I specifically recall taking the house car at Excelsior Galila in Milan (Maserati, as noted above), StR Rome (a super cool vintage Fiat 600 Multipla, which unfortunately they've retired), and RC Hong Kong (don't remember the vehicle). There have been others as well but I can't recall details.

I would define a "house car" as one that's available for guest use without charge. My definition would not include paid car service, which many properties offer, usually through a contractor but occasionally with their own vehicle(s).