Certificate of Authenticity

There is a wealth of confusing information about this.

What information do you include in a Certificate of Authenticity?
What makes a Certificate of Authenticity "authentic"?
Is it common practice to provide one?

I'm not sure what a certificate of authenticity is. Affixed to the back of my matted prints is a sticker with this statement: "This is a handmade, silver-gelatin photographic print, toned in selenium, and air dried. It has been processed to archival standards. No digital procedures were used in making it." The sticker is signed and also appears on the cardboard backing that one can read behind the frame. That's all I imagine could possibly be necessary unless or until I were dealing with collectors who might want more information separate from the print itself.

I could be wrong... But I'm sure I read somewhere once that certain US states (California rings a bell) had legal requirements for what had to be on the 'certificate of authenticity', specifically if you were selling prints as a limited edition.

Which is a long way of saying - it might be worth checking any local state laws/regulations?

This link was from another thread a while ago, though I can't speak for the accuracy of the text: http://www.collegeart.org/guidelines/photolaw.html