All products made from precious metals are legally certified by INCM - Contrastaria do Porto.

The application of contrast marks is only mandatory in silver pieces weighing more than 2 grams and gold pieces weighing over 0.5 grams.

You can check the table with the legal marks here:

INCM - Contrastaria

In case of doubt all consumers can verify the accuracy of each brand in INCM.
Daily gold and silver quotations are available here.