How to read official Swiss hallmarks, trademarks, collective responsibility marks and other things found in gold and silver watch cases
http://www.vintagewatchstraps.com/swisshallmarks.php
Schlagwort: case marks
Marks in watch cases – hallmarks, sponsor’s marks, etc.
Marks found in watch cases such as hallmarks, sponsor’s mark, date letter, assay office mark
http://www.vintagewatchstraps.com/casemarks.php