A system I'm playing with copies something called PI/Open.
A file inside this system is actually stored as a directory at the OS level, and it created filenames of the form <space><backspace>nnn.
I copied this, and found that Midnight Commander was great at managing the resulting files :-) It's done so that people can't tamper - corrupting one of the (many) OS-level files would do serious damage to the PI file.