In BFS (Be(OS?) File System) you can add any kind of attribute to a file, for what I know. Unfortunally, this isn't very helpful - since you need to run either

In BFS (Be(OS?) File System) you can add any kind of attribute to a file, for what I know. Unfortunally, this isn't very helpful - since you need to run either BeOS or Haiku. If I'm not mistaken, there's a FUSE port of BFS to Linux as well.