I totally agree with the last row of your article, but as a person who works for a company that specializes in digital signatures, I must tell you that many of our clients choose to invest in a 3 party digital signature solution in order to avoid that kind of "pranks" from their clients and colleagues.
If you're interested, there's some useful background (non-commercial) information about digital signatures at http://www.arx.com/digital-signatures-faq.php.

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