FAT has a "hidden" flag, which works under windows unless you poke through the folder settings to show hidden files (which I tend to do as a 'standard thing' on new windows computers :P). I dont know if UNIX FAT or Mac OS would support that flag, unix standard is to prefix hidden stuff with a dot, mac I have no clue (or care) about but probably works the same as unix since it is.
None of this covers your requirement that "new files written to the device are hidden", short of educating the users how to hide them. Which empowers them with the knowledge to undo what you've done anyway.
At a technical level, what you're asking a filesystem to do is counter to the design of most filesystems where the "index of the disk" is a very key and central structure, without encryption even in a filesystem like NTFS, your inability to browse a directory is something programatically enforced by that operating system, an open source file system driver can choose to pay no attention to such access 'hints', and ultimately you're just not going to achive anything anywhere near secure without a) a file system explicitly designed for this (unlikely in a decades old FS), or b) encryption software to render the data visible but unreadable. There are many many solutions to that, which would be a different question where you'd explain WHY you're trying to do something this weird.
I, for one, am glad no such capability exists, I'd refuse to use a filesystem that had any significant methods for hiding data on my own devices in a way I couldn't trivially find. That's for the realm of hacking / root kits and so forth to figure out, and the rest of us to prevent. IMHO.