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The Telerik UI ASP.NET AJAX RadSignature allows you to integrate it inside a form and validate the Signature before the form is submitted.

The content of RadSignature control can be conveniently validated with a asp:CustomValidator control.

Initially empty RadSignature has no value -> signatureObject.get_value() returns undefined. When the control is focused it gets a default value representing the blank background of the signature pad.

<telerik:RadSignature runat="server" ID="RadSignature1" Width="170px" Height="250">
    <ClientEvents OnLoad="signatureLoad" />

<asp:CustomValidator runat="server" ErrorMessage="*Signature is required" ForeColor="Red" ClientValidationFunction="validateSignature" EnableClientScript="true" />

<telerik:RadButton runat="server" ID="RadButton1" Text="Submit" Primary="true" AutoPostBack="true" />
var signature;
var focusedSignatureDefaultContent;

function signatureLoad(sender, args) {
    signature = sender;
    var innerElement = $telerik.$(signature.get_element()).find('.k-signature-canvas')[0];
    $(innerElement).focus(function () {
        if (!signature.get_value()) {
            setTimeout(function () {
                if (signature.get_value()) {
                    focusedSignatureDefaultContent = signature.get_value();

function validateSignature(source, args) {
    signature = $telerik.findControl(document, "RadSignature1");
    if (signature.get_value() && signature.get_value() !== focusedSignatureDefaultContent) {
        args.IsValid = true;
    } else {
        args.IsValid = false;

Test the Form Integration example in our live demo Signature Form Integration.

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