Hi,
Normally you have the HIKASHOP_NO_RESULT translation key that should be displayed on the page when no results are found after using the filter system.
It's displayed by that code in the product/listing.php view file:
} elseif(( !$this->module || hikaInput::get()->getVar('hikashop_front_end_main',0) ) && ($ctrl == 'product' || $ctrl == 'category') && $task == 'listing' && !empty($this->filters) && count($this->filters) && !empty($this->filter_set)) {
if(!empty($htmlFilter))
echo $htmlFilter;
echo JText::_('HIKASHOP_NO_RESULT');
}