Open your theme’s function.php and add the following code. Remember changing text after equal sign with your own.

function custom_content_after_post($content){
if (is_single()) {
$content .= ‘<p>Load Your Content Here</p><img src=”‘. get_template_directory() .’/images/signature.png” alt=”Your Name” />’;
}
return $content;
}
add_filter( “the_content”, “custom_content_after_post” );

You may also use WordPress Signature Plugin for doing so. It allows WP users to put signatures below every post. After installing and activating it you can easily access it by navigating to WP-Admin Dashboard >> Tools >> WPSignature.