De acordo com a documentação coreutils em --classify
(alias %código%),
-F
é para sockets:
Append a character to each file name indicating the file type. Also, for regular files that are executable, append ‘*’. The file type indicators are ‘/’ for directories, ‘@’ for symbolic links, ‘|’ for FIFOs, ‘=’ for sockets, ‘>’ for doors, and nothing for regular files. Do not follow symbolic links listed on the command line unless the --dereference-command-line (-H), --dereference (-L), or --dereference-command-line-symlink-to-dir options are specified.