The $folder thing is used by some other tool but not mine. To put a node that looks like a folder to s3sync you'd have to make a file with the exact content:
{E40327BF-517A-46e8-A6C3-AF51BC263F59}
That hashes to the MD5 that s3sync recognizes as a folder. Don't try to use my stuff to make folders that other tools will play nice with; there's no standard and no one does it the same way. (my way is best
But what I don't get is, why do you care? There's no reason to invent empty folders. Just store whatever/path/you/want/keyname.