I was not able to get the signatures to show up on the forum with the latest BuddyPress. I have the profile field "Signature" enabled and sitewide forums enabled (via http://codex.buddypress.org/user/setting-up-a-new-installation/installing-group-and-sitewide-forums/).
I was stumped, but I believe I found an error in the code.
The above line is repeated on line 157 and line 223. It seems it should only be used once. I changed line 157 to...
Now the plugin works perfectly with BuddyPress. I'm pretty sure you could edit either line or change it to any bp_has_ function that is always true.