Hook for signature changes?

[sinucello]

Hi,

I have a little plugin that informs us, whenever a user changes certain fields of his profile:

		<hookname>userdata_postsave</hookname>
			<phpcode><![CDATA[if ($this->condition)
{
	$olduserinfo = $this->existing;
	
	$newuserinfo = array(
		'field13' =>  '',
		'field14' => '',
		'field15' => '',
		'field16' => '',
		'field7' => '',
		'field17' => ''
	);

but the signature field doesn`t seem to be covered by this hook? What hook would be the right one for signature changes?

Thank you - all the best,
Sacha