Just a short one, without any CP thing:
In functionc.php find:
PHP Code:
global $counter,$firstnew,$sigcache,$highlight,$postid,$forum;
replace it with:
PHP Code:
global $counter,$firstnew,$sigcache,$highlight,$postid,$forum,$thread;;
Then find (in functions.php):
PHP Code:
if ($post[showsignature] and $allowsignatures and trim($post[signature])!="" and ($bbuserinfo[userid]==0 or $bbuserinfo[showsignatures])) {
replace it with:
PHP Code:
if (($thread[forumid]!=21) AND $post[showsignature] and $allowsignatures and trim($post[signature])!="" and ($bbuserinfo[userid]==0 or $bbuserinfo[showsignatures])) {
where 21 is the number of the forum where you don't want to show signatures.
If you know a little bit about php you now know how to add more forums to this list.