I've only found out as my new 120 - 400 comes within the problem serial numbers. There seems to be an issue with a few sigma lenses and the AF on them. I'm not sure if this has be posted already. The top answer covers the decoding of the letters very well. (also branded as: Pro-Optic Rokinon Bower).Descriptions by Lens FeaturesIf you know what feature you're looking for in a lens (cropped-frame designation ultrasonic motor, low-dispersion elements, image stabilization, etc.), and want to know what each of the brands call that feature, the following answers are organized by lens feature. Such lenses tend to follow the most stringent quality guidelines, and often come with a price premium.Off-Brand LensesMost off-brand lens manufacturers make lenses that fit many types of bodies, including Canon, Nikon, etc. Descriptions by Lens Make Brand LensesAll major camera manufacturers offer their own line of lenses. The historical answer has been broken up into individual answers per lens brand, with links to each of the lens brand answers below. When looking at a lens name, there are a lot acronyms describing its features (often specific to the manufacturer).Examples, Nikon:Nikon AF-S DX 16-85mm VR f/3.5-5.6G IF-EDNikon AF-I 600mm f/4D IF-EDNikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-EDExamples, Canon:Canon EF 85mm f1.2L USM Mark IICanon 70-300mm f/4.5-f/5.6 DO ISExamples, Sigma:Sigma 150mm F2.8 EX APO DG HSM MacroSigma 70-200mm F2.8 EX DG OS HSMSigma 50-150mm F2.8 EX DC APO HSM IIHow do I decipher these lens codes from different manufacturers? Note: Because of the community-wiki nature of this question, this accepted answer became really long, and difficult to edit and keep current as lens designations evolved. When you’ve finished, select OK to go back to the AF Microadjustment screen. If the number is not visible and you just see a series of zeros, use the Set button and main dial to enter the correct number. Press the Info button again to review the lens information and check its serial number.

Scr - Number of screws in the lens mount, useful for identifying pre-AI and AI versions 5- = 5 slot screws 3+ = 3 cross-head screws etc Notes - Identifying features of the lens and points of interest Start No - Serial number of first lens made Confirmed - Earliest and latest serial numbers seen ^ lens added to list in last 6 months. It appears that the lens you received is a 'Gray Market' lens, and has been tampered with having its serial number changed. The lens you received has a serial number which has not been issued by Sigma’s factory in Japan. The lens I received is a XXmm f/XX lens for my XXXXX brand camera, and has serial number #233XXXX.

Sigma lens serial number check