Source

File: wp-includes/general-template.php

function has_custom_logo( $blog_id = 0 ) {
	$switched_blog = false;

	if ( is_multisite() && ! empty( $blog_id ) && get_current_blog_id() !== (int) $blog_id ) {
		switch_to_blog( $blog_id );
		$switched_blog = true;
	}

	$custom_logo_id = get_theme_mod( 'custom_logo' );

	if ( $switched_blog ) {
		restore_current_blog();
	}

	return (bool) $custom_logo_id;
}