if (($("#tb_standard_reason").val().trim().indexOf('<') > -1 ) || ($("#tb_standard_reason").val().trim().indexOf('&#') > -1 )) {
    problems += '* Please do not include any HTML characters (<, >, or &#) in the reason.<br />';
}

/*
<asp:CustomValidator runat="server" Display="Dynamic" ErrorMessage="<br />*Please do not include any HTML characters (<, >, or &#) in the special situation details." EnableClientScript="true" ClientValidationFunction="validateInsecureCharacters" ControlToValidate="tb_SpecialSituationDetails" />
*/

function validateInsecureCharacters(source, arguments) {
    if ((arguments.Value.indexOf('<') > -1) || (arguments.Value.indexOf('&#') > -1)) {
        arguments.IsValid = false;
    } else {
        arguments.IsValid = true;
    }
};