[scarex80]

$maxsigweight=40000;
;
function check_sig_size($sig)
{
    global $maxsigwidth, $maxsigheight, $maxsigweight, $errors, $vbulletin;
    $sig = str_replace(array('  ', '\\"'), array('', '"'), $sig);
    $ary_header = get_headers($sig, 1);                  
    $imgdimension = $ary_header['Content-Length']; 
    
    if ($imginfo = getimagesize($sig))
    {
        if ($imginfo[0] > $maxsigwidth or $imginfo[1] > $maxsigheight or $imgdimension>$maxsigweight)
        {
            $vbulletin->GPC['preview'] = 'true';
            $errors[] = fetch_error('signaturetoobig', $maxsigwidth, $maxsigheight,$maxsigweight);
        }
    }
}

With the addings in red, I'm now able to check even the size in bytes of the images It works on 3.6.8