How to Add Signature or Ads after Post Content in Particular Category?

function custom_content_after_post($content){

if (is_single()) { 

    $content .= '<p>Load Your Content Here</p><img src="http://imgur.com/asdafe" alt="Your Name" />';

}

    return $content;

}


add_filter( "the_content", "custom_content_after_post" );

I got this code to insert to every post but how to insert different signatures in different categories ?