Detect inputs & textareas that use the required data annotation, attaches an asterisk to labels associated with them & replaces the legend indicating the asterisk's meaning.

jquery.requiredfields.js

/*
 * jquery.requiredfields.js
 * Copyright (c) 2012 Adrian D. Alvarez
 * Licensed under the MIT, GPL licenses.
 */
(function ($) {

    var requiredlegend = "Essential information is marked with an asterisk (<abbr title='Required' class='required'>*</abbr>)";
    var requiredlegendset = false;

    $("input,textarea").each(function (i) {
        if ($(this).attr('data-val-required')) {
            var id = $(this).attr('id');
            var requiredlabel = $("label[for=" + id + "]");
            var requiredlabeltext = $(requiredlabel).text();
            $(requiredlabel).html(requiredlabeltext + " <abbr title='Required' class='required'>*</abbr> ")

            if ($("fieldset:contains(" + $(this) + ")") && (requiredlegendset === false)) {
                //Replace existing legend
                $("fieldset").has(this).find('legend').html(requiredlegend);

                requiredlegendset = true;

            };
        };
    });

}(jQuery));