The Department of State has announced that several individuals and vessels have been added to the Department of Treasury's List of Specially Designated Nationals and Blocked Persons. This action is part of enforcing an Executive Order aimed at blocking property related to harmful activities by the Russian government. As a result, all property and interests in the US linked to these people are blocked, and American citizens generally cannot do business with them. The vessels listed are linked to various Russian entities and are subject to these sanctions.
Simple Explanation
The U.S. government has identified people and boats connected to harmful activities by the Russian government, so they have been put on a special list. This means their things in the U.S. are frozen, and people in the U.S. can't trade with them.