The domain in the URL can help. If it's a United States website, the url will have .gov as the domain.

If it's a government site outside the U.S., it may have .gov and then the country initials. For example, here is Turkey's:

This practice for international governments, while popular, is not universal.

Government Documents

• What is the agenda of the government in question?
• What government agency produced it and what is the purpose of that agency?