There's a file called
MM! in every directory in DOS 6.22. Just
MM!, no file extension... What causes this?
If your DOS 6.22 system has network file-sharing enabled and it's file-shares are accessed from a Windows system that is running some file management/cataloging software, it is possible the software creates the "MM!" files to keep track of some metadata such as the archiving policies for each folder or a history of actions taken.
This is pure speculation based on Googling for "MM file", noting certain interesting results and thinking about the way products like Picasa (not the culprit) create metatdata files in each folder.