Add the bb-signatures.php file to bbPress' my-plugins/ directory.
Activate and check under "Site Management" admin submenu for "Signatures".
If you would like the optional toggle on new/edit posts to allow the member to disable signatures on a per-post basis,
you must edit the edit-form.php & post-form.php templates and place at or near the bottom:
(you can optionally wrap that in a DIV and float it to the left, right style anyway you'd like)