onSign for

From onSign.com:

With onSign, you can securely embed your personal, handwritten signature into your Word documents or Outlook messages with a simple click of your mouse. onSign uses industry standard SHA-1 and RSA algorithms to lock your signature to the contents of a document, making your signature invalid if even one character in the message is changed. Your signature cannot be copied, removed or altered, giving you the freedom to express your identity in your electronic communications. onSign is free, downloadable, and the only secure way to reclaim the power of your personal signature. Best of all you can capture your electronic signature with your Palm and use it on your PC!