No Salt
The figure for "salt" on a European label is calculated from sodium: sodium × 2.5. This value includes not only salt that the manufacturer added separately, but also sodium from other ingredients. The calculation is established by Regulation (EC) No 1169/2011.
The perk takes this number per 100 g of product.
0 g is the lowest displayed level. A small amount of salt may still be rounded to zero on the label.
Any value above zero indicates "contains salt". If it's more than 1.5 g per 100 g, the perk writes "high in salt". This is the same threshold used for the 'high' level in UK FSA labelling. For beverages, the FSA has a separate threshold – more than 0.75 g per 100 ml.
If you are looking for a product with minimal salt, look not only at the perk's message but also at the number itself. Yogurt with 0.1 g of salt will get "contains salt", as will a sauce. But these are completely different amounts of salt in a real serving.
The 100 g figure is primarily for comparing products. You don't eat "100 g of product", but a specific portion. 100 g of soy sauce and 100 g of bread look the same in a table, but usually a very different amount ends up on your plate. Therefore, a product "high in salt" does not necessarily provide a lot of salt per meal – it all depends on the portion size.
For adults, the WHO recommends consuming less than 5 g of salt per day. 100 g of a product with 1.5 g of salt is already about a third of this guideline.
Look at the perk's message, but to assess your diet, also consider the portion size.