That's exactly what I wondered after putting up the post below. So I checked it out.

According to this site, Poor Man's copyright is as follows:

A scheme by which you mail your manuscript in a sealed envelope to yourself via registered U.S. Mail. The belief is that, since the sealed envelope bears the government stamp (that of the U.S. Postal Service), an official record has been created of your creation of the work. If it comes to a court case, the envelope is submitted as evidence, the seal broken, and proof thereby obtained of a date of creation (the date of the postmark). While this can possibly be used as evidence of creation, it does not provide the monetary awards made available by true registration.

No matter what medium you're operating in, poor man's copyright is absolutely no guarantee of copyright. If you want to give it a shot, Copyright Authority.com breaks down in detail exactly what the copyright is and how to do it. And helpfully, it also notes, "A poor mans copyright could leave you even poorer, if that's all you have as proof of copyright"

Basically, it sounds like a poor man's copyright is potentially risky business. You might be a poor writer, but hopefully you're not so poor as you can't scrounge up $30 to pay for a real copyright.