Quick answer
The Hermès Plume is a flat, light bag. Hermès lists sizes in centimeters, most often 20, 28, 32, and 40. "MM" is not the label on the box. It is a term resellers and replica sellers use, most often for the 32 cm. Three checks catch most fakes: stitch type, heat stamp, and date stamp.
What the Plume MM is
Plume means feather in French. The name refers to weight. The bag has a slim profile, two handles, and a flat body. Hermès has made it in box calf, Togo, Swift, and Epsom. Production varies by year, and Hermès retires colors and leathers without notice. A listing that names a leather the model never used is a warning sign.
Check 1: stitching
Hermès artisans sew by hand with two needles and one waxed thread. This is a saddle stitch. The stitches sit at a slight angle and hold tension if one thread breaks. Machine stitching makes a lock stitch: two threads looped through each other, uniform, and flat. Look at the top edge and the handle attachments. On a real Plume, hand stitches run in a straight line with even spacing. Fakes show machine stitches, uneven spacing, or glue along the edge.
Check 2: heat stamp
Authentic bags carry "HERMÈS PARIS" and "MADE IN FRANCE" in foil or blind. Letters are sharp. Spacing is even. The accent on È is present. Fake stamps blur, sit crooked, or use a plain E. Placement changes with model and year, so compare against a known real bag from the same era.
Check 3: date stamp and hardware
Hermès bags have no serial number plate. They have a blind date stamp: a letter inside a shape, plus a craftsperson code. Location and format changed over the decades, and Hermès does not publish a decoder. Hardware is brass with gold or palladium plating. It does not stick to a magnet. Engraving is crisp. Fake hardware often sticks to a magnet and shows shallow, rounded engraving.
Legal position in the US
Selling counterfeit goods is a federal crime under 18 U.S.C. § 2320. First-offense penalties reach 10 years and $2 million for an individual. Trademark owners can also sue under the Lanham Act. CBP seizes counterfeit imports and destroys them. Hermès enforces its marks, including the name, the H hardware, and the Bolduc ribbon.
What cannot be verified
Hermès does not publish an authentication guide or a date-code database. No third party holds an official code list. Paid authentication services keep private records. If a seller claims a "registered serial number" on a Plume, that claim has no basis.