Signs educating visitors about the nation's past have been a key element of our national parks and historic sites. But following an executive order from President Trump, the Department of the Interior has removed dozens of signs that the administration claims promote "divisive narratives" and "corrosive ideology" – information on such topics as race relations, slavery, women's history, Indigenous peoples, and climate change. Hundreds more signs, books and pamphlets have been flagged for review. Jim Axelrod looks at efforts to remove lessons about America's complicated past.