crescendo,
First, check and see if the line doesn't show up on both threaded and flat mode, since they are coded separately.
Next, look at your showflat.php and post the code you have beginning with:
code:
if ($Signature) {
$Signature = str_replace("\n","<br />",$Signature);
then post the next 4 lines.
In your showthreaded.php, find those same lines, and post the next 4 lines. That might help someone see where the error could be.