site_admin_notice()

function site_admin_notice() {
	global $wp_db_version, $pagenow;

	if ( ! current_user_can( 'upgrade_network' ) ) {
		return false;
	}

	if ( 'upgrade.php' == $pagenow ) {
		return;
	}

	if ( get_site_option( 'wpmu_upgrade_site' ) != $wp_db_version ) {
		echo "<div class='update-nag'>" . sprintf( __( 'Thank you for Updating! Please visit the <a href="%s">Upgrade Network</a> page to update all your sites.' ), esc_url( network_admin_url( 'upgrade.php' ) ) ) . "</div>";
	}
}