International standards
Boats intended to be sold in the European Union are required to meet CE standards, which include rating them for the number of people and type of service. This number can be found for many boats, and must be on the builders plate in the EU. It will read something like A6 B7 C8 D10: meaning rated for 6 people in the ocean, 7 offshore, 8 coastal and 10 in protected waters, On the other hand, like ISO 9001, it primarily reflects a set of mechanistic criteria and probably has precious little to do with real seaworthiness. That being said, if a boat were not rated for offshore, it might not be too smart to take it there.