Validate Checkbox using Custom Validator

Validate Checkbox using Custom Validator : Here is the Html code:

Here is the .cs Code :

protected void chkSignaturecheck(object source, ServerValidateEventArgs args)
  {
     if (chkSignature.Checked)
     {
       args.IsValid = true;
     }
     else
     {
       args.IsValid = false;
     }
  }

Here is the output