If one wants to read the resulting signature server-side (after a button-click / form submission), one kind of has to work with a lot of javascript and hidden input fields to transfer the base64-encoded png towards the server. It would be way nicer if you could provide the content of the signature as a server-side property of the RadSignature-control (during post-back).
As Doncho mentioned in this related thread, those base64strings could be quite large.
Maybe it would be an option to have the base64string in the viewstate if and only if a flag is set at the control to specifically enable this feature. This way each programmer could configure this on case by case basis - just a thought.