[Xenon]

easiest way:

open admin/functions.php
find:

PHP Code:

if ($post[showsignature] and $allowsignatures and trim($post[signature])!="" and ($bbuserinfo[userid]==0 or $bbuserinfo[showsignatures])) {
            if (!isset($sigcache["$post[userid]"])) {
                $post[signature]=bbcodeparse($post[signature],0,$allowsmilies);
                eval("\$post[signature] = \"".gettemplate("postbit_signature")."\";");
                $sigcache["$post[userid]"] = $post[signature];
            } else {
                $post[signature] = $sigcache["$post[userid]"];
            }
        } else {
            $post[signature] = "";
        } 


and replace with this:

PHP Code:

if (($post[usergroupid]==6 or $post[usergroupid]==5 or $post[usergroupid]==7) and $post[showsignature] and $allowsignatures and trim($post[signature])!="" and ($bbuserinfo[userid]==0 or $bbuserinfo[showsignatures])) {
            if (!isset($sigcache["$post[userid]"])) {
                $post[signature]=bbcodeparse($post[signature],0,$allowsmilies);
                eval("\$post[signature] = \"".gettemplate("postbit_signature")."\";");
                $sigcache["$post[userid]"] = $post[signature];
            } else {
                $post[signature] = $sigcache["$post[userid]"];
            }
        } else {
            $post[signature] = "";
        }