China

Factory 11

using double diamonds as symbol

Factory 20

 using a square inside a cirkel as symbol

Factory 60A

early headstamp (untill 1955)

later headstamp (from 1956 onwards)

Final version

Besides the various characters for the factory and 30 for the caliber, also month and year of production are included in the headstamp for most chinese factories. For the months, following characters are used:

Examples of the month codes at the 6 O'clock position (April & May missing)