All the pieces made in precious metals are hallmarked according to the legal regime for goldsmiths and assay offices.

Assay offices are official and technical services that are responsible for assaying and marking articles of precious metal, as well as for placing legal fineness hallmarks on these articles.

Each piece of jewelry made in precious metals contains responsability mark and assay office hallmark (if the weight of the piece requires) identifying type of metal and its legal fineness. 

Responsibility marks consist of an engraving with a unique and exclusive design, accompanied by a letter. They are used to identify the organisation responsible for placing the article of precious metal onto the market.

The legal hallmarks of the Portuguese Assay office can be consulted HERE

In case of doubt about the authenticity of the marks, you can use, for verification purposes, the services of the Assay office. 

Information on daily quotations provided by Banco de Portugal