ambigram
noun
am·bi·gram ˈam-bə-ˌgram 
plural ambigrams
: something (such as an image of a written word or phrase) that is intended or able to be oriented in either of two ways for viewing or reading
When flipped upside down, it can create the same image, or may form a new image entirely. A very basic ambigram is the word "mom" which can be flipped to say "wow."
Sara Gadzala
Sara Gadzala… we created ambigrams and printed the ads upside down in magazines. At first glance, the reader sees a positive phrase. But when the ad is inverted, the copy reveals a sentiment quite the opposite … Michael Zhang
Michael Zhang
Word History
Etymology
ambi- + -gram
Note: The word was apparently introduced by the author and cognitive scientist Douglas R. Hofstadter (born 1945) in chapter 13 of the book Metamagical Themas: Questing for the Essence of Mind and Pattern (New York, 1985).
First Known Use
1984, in the meaning defined above