The Speedy is a single piece of canvas wrapped under the bag, which is the fact that decides most Speedy cases. Because one length of canvas runs from the front, under the base, and up the back, the monogram is necessarily upside down on one of the two faces. A Speedy with both faces the right way up has been made from two cut panels, and Louis Vuitton does not make it that way.
The handles are the second read. They are rolled vachetta, firm rather than floppy, and they darken years before the piping does. On a genuinely old Speedy the handles will be several shades ahead of the trim on the base — an even tone across both is the signature of a bag that was dyed rather than carried.
Sizes are numbered in centimetres across the base: 25, 30 and 35 are the classics, with the 40 and 45 as travel pieces. The Bandoulière variant adds D-rings and a strap and is a distinct reference, not an aftermarket addition, so a strap fitted to rings that were riveted on afterwards is a modification at best.
The lock is brass, numbered, and swings on its own tab; it is decorative and not a security feature. Locks are interchangeable between bags, so a mismatched lock number is not evidence of a fake — but a lock that is light, bright yellow, or stamped shallowly is.
References and sizesSpeedy 25 · Speedy 30 · Speedy 35 · Speedy Bandoulière
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.