protected function generateTags(Signal $signal)
    {
        $tags = [];

        if (isset($signal->contentId)) {
            // self in all forms (also without locations)
            $tags[] = 'content-' . $signal->contentId;
            // reverse relations
            $tags[] = 'relation-' . $signal->contentId;
        }

        if (isset($signal->locationId)) {
            // self
            $tags[] = 'location-' . $signal->locationId;
            // direct children
            $tags[] = 'parent-' . $signal->locationId;
            // reverse location relations
            $tags[] = 'relation-location-' . $signal->locationId;
        }

        if (isset($signal->parentLocationId)) {
            // direct parent
            $tags[] = 'location-' . $signal->parentLocationId;
            // direct siblings
            $tags[] = 'parent-' . $signal->parentLocationId;
        }

        return $tags;
    }