Short answer. Not for negotiability. If the document promises delivery to bearer or to a specified person or order, stamping it "not negotiable" does not stop it from being negotiated — it remains a negotiable document of title. What the marking may affect is the issuing bailee's own obligations.
What the law says
such document may nevertheless be negotiated by the holder and is a negotiable document of title within the meaning of this Title
Civil Code, Article 1510 — 'Not Negotiable' Marking. Read the full provision →
What the law says
nothing in this Title contained shall be construed as limiting or defining the effect upon the obligations of the carrier, warehouseman, or other bailee issuing a document of title or placing thereon the words "not negotiable," "non-negotiable," or the like
Civil Code, Article 1510 — 'Not Negotiable' Marking. Read the full provision →
The wording of the promise controls, not the stamp
A document of title — a bill of lading, a warehouse receipt, a dock warrant — is the paper that stands for goods held by a carrier or warehouseman. Whether it is negotiable depends on how the undertaking is written. If the bailee promises to deliver the goods to bearer, or to a specified person or order, the document is negotiable by its own terms. Article 1510 of the Civil Code says that adding a contrary label does not undo that: such document may nevertheless be negotiated by the holder and is a negotiable document of title within the meaning of this Title. The stamp does not rewrite the promise underneath it.
Why the law refuses to give the stamp that power
Commerce runs on the reliability of these documents. Goods in a warehouse or on a ship are sold, pledged and financed by transferring the paper rather than moving the cargo, and the person taking the paper must be able to judge what he is getting from the face of the instrument. If a single conflicting stamp could quietly strip a document of its negotiable character, every holder would have to investigate behind the words of the undertaking before parting with money. The rule protects the party who takes the document in good faith and for value, and it places the consequences of sloppy drafting on the party who issued it.
What the marking can still affect
The article does not treat the stamp as meaningless. Its closing sentence says that nothing in this Title contained shall be construed as limiting or defining the effect upon the obligations of the carrier, warehouseman, or other bailee issuing a document of title or placing thereon the words "not negotiable," "non-negotiable," or the like. In other words, the document's character as between holders is settled, but what the bailee has taken on by issuing it and marking it that way is left to the law and the contract governing the bailment. The marking may therefore matter a great deal to the bailee's exposure, without helping the party who wanted to block transfer.
The practical lesson if you are the one issuing it
If you genuinely do not want a document transferable, do not rely on a stamp. Draft the undertaking as a promise to deliver to a named person only, without the words "or order" or "to bearer" and without wording of similar import, and check that any form or template you use has not reintroduced them. Preprinted commercial forms are a common trap here. If you are on the receiving end and someone tells you a marked document cannot be transferred, the position may well be the opposite. Documents of title also interact with the rights of an unpaid seller and with pledge and financing arrangements, so bring the actual document to a lawyer rather than working from the label.