Moderators can only see the signature field
\applications\core\modules\front\members\profile.php
if ( ( \IPS\Member::loggedIn()->modPermission('can_modify_profiles') OR \IPS\Member::loggedIn()->modPermission('can_unban') ) AND \IPS\Member::loggedIn()->member_id != $this->member->member_id )
{
$form->add( new \IPS\Helpers\Form\Editor( 'signature', $this->member->signature, FALSE, array( 'app' => 'core', 'key' => 'Signatures', 'autoSaveKey' => "frontsig-" . $this->member->member_id, 'attachIds' => array( $this->member->member_id ) ) ) );
I think it's a bug because the setting (Enable Signatures?) is respected in many areas
E.g. ACP edit profile page
Result
Result