DVDInfo X 3 is a small utility that scans your Mac for DVD drives and displays their RPC (Region Playback Control) status. It supports multiple drives.
A RPC-1 (region free) DVD drive will play movies from any region.
A RPC-2 (region locked by the RPC Phase II scheme) DVD drive's region may be changed 5 times, then it will be locked.
Once locked, it can be reset by the manufacturer (or vendor), so you'll have 5 changes left, again. Only 4 vendor resets are allowed, then the drive will be definitely locked. It can only play movies authorized for the region it belongs to.