It is not totally unlimited (A TEXT column with a maximum length of 65,535 (216 – 1) characters.) but close enough for 95% of you

In /scripts/changebasic.inc.php
Find:
// If signature is greater than the specified size, do not allow
if ( strlen($Signature) > $config['SIGNATURE_LENGTH'] ) {
Replace with:
// If signature is greater than the specified size, do not allow
if ( strlen($Signature) > $config['SIGNATURE_LENGTH'] &&
( ($user['USER_MEMBERSHIP_LEVEL'] != "Administrator") && ($user['USER_MEMBERSHIP_LEVEL'] != "Moderator") ) ) {
Preview still says you are over, but this overrides the check for Admins and Mods
