[fel64]

Code like this:

add_filter('get_profile_info_keys', 'add_sig_key');

function add_sig_key( $keys ) {

$keys['sig'] = array(0, __('Signature'));

}

Just add that to the plugin file. It should probably work, but it’s a bit of a guess.

Much better to do it this way with a plugin than editing core files, too.