Under 10.4, my Dock icon for my internal hard drive was showing mach and mach.sym when control-clicked. This irritated me so I decided to check out .hidden in the root directory. To my surprise, that file has been removed under 10.4. On a hunch, I decided to recreate the file using pico. I entered this text exactly into the file (again, this is in the top-level directory):
And I restarted the system. Sure enough, after the restart, I found that 10.4 respects the file, even though it's no longer installed by default. Those files no longer appear in my Dock icon for the hard drive.
Mac OS X Hints