The Kelly took its name from Grace Kelly in the 1970s; the Birkin followed in 1984, after Jane Birkin met the Hermès chief executive Jean-Louis Dumas on a flight from Paris to London. Sotheby's notes that each Birkin is made by a single artisan over at least 18 hours and stamped with a code for its year and its maker. Because both bags are scarce at the boutique and valuable on the secondary market, they are also among the most counterfeited bags made, and the best copies are very good.
The blind stamp (date code)
Hermès dates its bags with a small embossed letter known as the blind stamp, usually on the interior flap, under a strap or on the side gusset, alongside a craftsman's mark. Rebag and other specialists describe four broad eras: a plain letter from 1945 to 1970, a letter in a circle from 1971 to 1996, a letter in a square from 1997 to 2014, and a plain letter again from 2015, when the stamp moved to a longer format with the date letter followed by craftsman characters. The square D, for instance, is 2000. Christie's points out that the stamp is meant to be subtle and that counterfeiters often press it too deeply. The year it gives must agree with the leather, colour and hardware the house was actually using then. Not every genuine Hermès piece carries a blind stamp, and a correct one proves nothing on its own: it is the easiest mark to copy.
The Hermès Paris stamp
On pieces made after 1965, the logo stamp reads "Hermès Paris Made in France", usually across three lines in type that grows smaller line by line. Christie's says it should be centred, evenly spaced and pressed cleanly into the leather, and that its colour usually matches the hardware (gold foil with gold hardware, silver with palladium, blind on some leathers). Misspelling, uneven lettering or poor alignment are immediate concerns.
Stitching and construction
Hermès bags are saddle stitched by hand with waxed linen thread, so the stitches sit at a slight, even slant and the thread is tight. The edges are sanded, painted and burnished. Look at the handles, the corners and the sangles: wavering lines, loose thread or glue at the edges point to a factory copy.
Hardware
The turn-lock, clochette, padlock and keys should be heavy and finely finished, with crisp engraving. The padlock and keys on Birkins and Kellys are numbered; the numbers should agree. Feet (clous) should be secure and identical. Plated hardware that is flaking or looks too bright on a bag described as older is a warning sign.
Exotics and paperwork
Exotic skins carry additional marks next to the blind stamp, which Sotheby's lists by skin, and should travel with the correct wildlife permits; Christie's notes that a crocodile or lizard bag without a permit is a problem in itself. Hermès does not issue authenticity cards. Christie's specialist is blunt: any Hermès product sold with one is fake. An original receipt is useful supporting evidence, but receipts can be forged too.
Packaging
The orange box, dust bag, rain cover, clochette and lock are all copied in quantity. Treat packaging as context, never as proof.
When to get a professional opinion
Any Birkin or Kelly offered for sale should be authenticated by a specialist before money changes hands. Christie's and Sotheby's authenticate each bag they sell through their own handbag departments, and resellers such as Rebag and The RealReal authenticate in house.
For a full year chart and lookup, see Hermès blind stamps.