Display order number in edit order page for WPMU DEV MarketPress plugin. Just add the code in functions.php file of your child theme or use it as mu-plugin.

mp-order-number-on-edit.php

<?php 
function wpmudev_mp_sho_order_number( $post ){

	if( 'mp_order' != get_post_type( $post ) ) return $post;

	echo '<h1 class=&quot;order_number&quot;> # ' .$post->post_title . '</h1>';

	echo '<style>
		h1.order_number{
			margin-top: -42px;
    		margin-left: 104px;
		}
	</style>';

}
add_action('edit_form_top', 'wpmudev_mp_sho_order_number');