<style>
        .container {
            position: relative;
        }

        .overlay {
            width: 100%;
            height: 100%;
            position: absolute;
            top: 0;
            left: 0;
            opacity: .2;
            background-color: #6495ed;
            text-align: center;
        }

            .overlay div {
                position: relative;
                font-size: 34px;
                margin-top: -17px;
                top: 50%;
            }
    </style>
...
        <div class="container">
            <div class="overlay"><div>No data available</div></div>
                <telerik:RadHtmlChart ID="RadHtmlChart2" runat="server">
                    <ClientEvents OnLoad="onChartLoad" />
                </telerik:RadHtmlChart>
        </div>
        <script>
            var $ = $ || $telerik.$;

            function onChartLoad(chartO, args) {
                var chart = chartO.get_kendoWidget();
                var view = chart.dataSource.view();
                $(".overlay").toggle(view.length === 0);
            }
        </script>