Replace Image URL in functions with Directory image

[jacquisdesigns]

I'm trying to add a signature to the functions.php and would like to replace the uploaded image with an image that's in the theme directory. is this possible?

CODE:

// Add Signature Image after single post
add_action('genesis_after_post_content', 'custom_include_signature', 1);
function custom_include_signature() {
if(is_single()) { ?>
<img src="IMAGE" alt="Signature" />
<?php }}

I would like to replace the <img src="IMAGE" alt="Signature" /> with something like this: (images/signature.png)

thank you