Occasionally I will get a request to do something that I simply am not authorized to do as a Colorado notary public. Today was such a day, and a Medallion Signature Guarantee is such an act.
The man told me that it was for transferring stock between himself and his father. It reminded me of the time when I had a stock certificate that I wanted to transfer to my brokerage account so that the shares would be in "street name". I took the stock certificate to Wells Fargo, where I have an account, and one of the bank employees affixed a Medallion Signature Guarantee stamp. But this man told me that he didn't have a bank account. So he called me, hoping that I could help him.
Unfortunately I can't. Even if I owned a Medallion Signature Guarantee stamp, I am not authorized to guarantee a signature. Here is a sample of a Medallion Signature Guarantee imprint:
It must be done by a financial institution (i.e. bank, credit union, or broker dealer) that participates in one of the Medallion signature guarantee programs.
For more information, read: Signature Guarantees: Preventing the Unauthorized Transfer of Securities at the U.S. Securities and Exchange Commission website.