The ICC is the United Nations created International recreational sailing license. It was created under United Nations Resolution 40. All Yacht Charter Companies recognize the ICC as an international Sailing License. To gain an ICC you must be assessed by a Royal Yacht Association instructor of which there are very few in the USA and Canada.
A more accessible valid sailing license to get in North America is the SLC. The SLC is recognized by Yacht charter companies and port authorities worldwide just as much as the ICC. The accessibility of getting an SLC in other parts of the world is growing. See the NauticEd Sailing Schools and Instructors webpage.