can be found and was published on the IWC collectors forum and these hallmarks were already used from 1938 onwards on all imported watches.
`Importing the Ref 325s into Portugal Watches imported into Portugal from 1938 to 1985 were stamped with a distinctive hallmark (marca de contraste or just c ontraste) depending on the case metal. The law regulating the hallmarks actually dates from 1932 but it was only fully implemented in 1938. These hallmarks were applied manually , via a stamp (punção), during the impor-t ation process, at one of the regional Assay Offices (Con-t rastarias), which operated at the National Mint`
written by Antonio Gomes for the IWC forum , http://www.iwcforum.com/IWC.pdf