You can't miss the Morton Salt factory. Something about it... Oh right, the 3-story tall letters. This is one of the landmarks I always look for when I fly into Chicago.
Morton Salt has a long history in Chicago. The company which eventually became Morton Salt began here in 1848. In 1889 a controlling interest was sold to Joy Morton, who changed the name to Joy Morton and Co. In 1910 it became the Morton Salt Co. You might recognize the name Morton from their philanthropic additions to the city. Notably, the Morton wing of the Art Institute of Chicago. Probably the Morton Arboretum too, now that I think about it.
Visit the Morton Salt website and see the different versions of the girl with the umbrella.