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Manufacturer, part number and lot number. By looking up the manufacturer's datasheet for the part all electrical attributes can be determined. There are several numbering standards such as JIS, Pro Electron and JEDEC: Transistor - Wikipedia, the free encyclopedia.
From the transistor no. eg BC547, you can find out everything required about the transistor by referring to its datasheet. You can find the maximum voltage that can be applied, its gain, if it is NPN or PNP, the Vce(sat), storage time, pin layout, current capacity, maximum power dissipation, etc.