uniquify-separator

uniquify-separator is a variable defined in `uniquify.el'.
Its value is

nil

Documentation:
String separator for buffer name components.
When `uniquify-buffer-name-style' is `post-forward', separates
base file name from directory part in buffer names (default "|").
When `uniquify-buffer-name-style' is `reverse', separates all
file name components (default "\").

You can customize this variable.