A signature guarantee is a financial institution's assurance that a securities-transfer signature is genuine and properly authorized.
A signature guarantee is an assurance by an eligible financial institution that a signature used to transfer a security is genuine and that the signer is an appropriate person with legal capacity to sign. In U.S. securities transfers, the guarantee is commonly provided through a recognized medallion signature guarantee program.
It is not merely a visual comparison of signatures. The guarantor takes on specified warranties and potential liability if the guaranteed signature or authority is defective.
Under the Uniform Commercial Code framework, a person guaranteeing a signature on a security endorsement warrants that, at the time of signing:
Additional warranties can apply when an institution guarantees an endorsement or instruction rather than only the signature. This distinction is one reason the document, transaction type, and wording of the guarantee matter.
The guarantee does not mean that:
| Control | Main purpose | Typical provider | Securities-transfer liability |
|---|---|---|---|
| Signature guarantee | Warrants signature genuineness, authority, and capacity | Eligible financial institution | Yes, within the applicable guarantee framework |
| Medallion signature guarantee | Standardized securities-transfer guarantee under a recognized program | Participating bank, credit union, broker-dealer, or other eligible institution | Program and guarantor backing apply |
| Notarization | Verifies identity and acknowledges or witnesses signing under notarial law | Commissioned notary | Not the same transfer warranty |
| Witnessed signature | Confirms that a person signed in the witness’s presence | Eligible witness under the document rules | Usually no securities-transfer guarantee |
| Electronic authentication | Verifies account access or electronic instruction | Broker, transfer agent, or service provider | Depends on system rules and agreement |
A witness generally confirms that a person signed in the witness’s presence. The witness does not thereby assume the securities-transfer warranties or financial liability of a signature guarantor. The witness’s eligibility and the legal effect of witnessing depend on the document and applicable jurisdiction.
A notary performs a separate identity, acknowledgment, oath, or witnessing function under notarial law. Notarization can be required for many legal documents, but it does not create the signature, authority, and capacity warranties used in a securities transfer.
If a transfer agent requests a medallion signature guarantee, a witnessed or notarized signature generally is not a substitute. The investor should follow the receiving institution’s current written instructions rather than infer requirements from the document’s signature block.
A transfer agent or financial institution may request a guarantee for:
Requirements vary. Some transactions use electronic controls, broker messages, standing account instructions, or exceptions that make a paper guarantee unnecessary. Obtain the exact current instructions rather than assuming that every securities transaction requires a stamp.
Banks and brokers are not required to provide the service to every requester. An institution may decline because it cannot verify the ownership chain, signer capacity, transaction value, destination, or supporting documents.
Jordan owns a certificate for 400 shares and wants 100 shares registered to a sibling. The transfer agent instructs Jordan to submit the certificate, a stock power, and a medallion signature guarantee.
Jordan visits a participating bank where he has an established account, presents the unexecuted documents and proof of ownership, and signs as instructed. The bank guarantees Jordan’s signature on the stock power. The transfer agent still reviews the certificate, share amount, registration, restrictions, and other documents before recording the transfer.
The guarantee reduces signature risk, but it does not complete the transfer by itself. The issuer-level ownership record changes only after the transfer agent accepts and processes the package.
This article is educational only and does not provide legal, tax, estate, compliance, or investment advice. Follow the receiving transfer agent’s current instructions for the specific security and transaction.