
WHAT IS AN AMBIGRAM?
An ambigram is a visibly symmetrical word, calligraphic design, art form, or any other type of symbol that retains a certain meaning regardless* of the direction, perspective, or orientation from which it’s viewed. The meaning of the ambigram can either change or stay the same.
The word combines Latin ambiguus [“having double meaning, shifting, changeable, doubtful,"] with gram which is derived from Greek graphein [“to draw, write.”]
EXAMPLES
All examples are rotated by 180 degrees. *I found no visibly symmetrical examples where the picture appears the same from all four directions, i.e. regardless of orientation.
HISTORY
● Recent
Artist Peter Newell drew the first ambigrams and included these “invertible illustrations” in his series of “Topsys and Turvys” books starting in 1893. One of his most popular illustrations reads “Puzzle” in one direction and “The End” upside down. Newell is known for the illustrations he created for famous authors like Mark Twain and Lewis Carroll.

Image source: https://en.wikipedia.org/wiki/Ambigram
In the early 1900s, Dutch-American comic artists Gustave Verbeek also used ambigrams in three consecutive strips. According to Wikipedia, “His comics were ambiguous images, made in such a way that one could read the six-panel comic, flip the book and keep reading.”
Four years late, in 1908, British monthly “The Strand Magazine” also published ambigrams drawn by different people.
Indiana professor Douglas Hofstadter and some of his friends coined the word ambigram in the 1980s and introduced what might be called today’s modern ambigram. The movie “Angels and Demons” popularized the word.
Ambigrams are not exclusively in English. They exist in other languages and other alphabets, and the concept can be applied to numbers and other symbols besides words.

The term may have been coined recently, but mirror ambigrams date back to the first millennium as palindromes designed to be visually symmetrical. In ancient Greece these were referred to as something like mirror writing.
Image credit: Gregory of Nazianzus
Photo Credit: Christine Kekka, Athens, Light corrections by Basie Morin,
Image source: http://commons.wikimedia.org

Mikrror ambigram ΝΙΨΟΝ ΑΝΟΜΗΜΑΤΑ ΜΗ ΜΟΝΑΝ ΟΨΙΝ (Wash your sins, not only your face,)
Written in Greek in the church Hagia Sophia, (Turkey) 380 AD..
Image Source: commons.wikimedia.org/wiki/File:Sator_Square
Today, there are over a dozen different types of ambigrams. The following definitions taken from Wikipedia. https://en.wikipedia.org/wiki/Ambigram

A word or number that is an ambigram naturally, without any additional formatting. For example: dollop, suns, pod, swims, and bud.

Two interpretations are seen when the image is rotated 180 degrees with respect to each other (in other words, a second reading is obtained from the first by simply rotating the sheet).

A symmetrical ambigram can be called "heterogram" when it gives another word. Visually, a heterogram ambigram is symmetrical only when both versions of the pairing are shown together.

"Half-turn" ambigrams or point reflection ambigrams, commonly called "upside-down words", are 180° rotational symmetrical calligraphies. We can read them right side up or upside down, or both. Rotation ambigrams are the most common type of ambigrams for good reason. When a word is turned upside down, the top halves of the letters turn into the bottom halves.

A mirror ambigram, or reflection ambigram, is a design that can be read when reflected in a mirror vertically, horizontally, or at 45 degrees, giving either the same word or another word or phrase. When the reflecting surface is vertical (like a mirror for example), the calligraphic design is a vertical axis mirror ambigram.

When the reflecting surface is horizontal (like a mirroring lake for example), the calligraphic design is a horizontal axis mirror ambigram.

In a figure / ground ambigram, letters fit together so the negative space around and between one word spells another word. A design that utilizes the spaces between letters to form additional words.

An object that appears to have several different letters or words depending on the viewing angle.

Where words and letters are interlinked, sometimes overlapping, to form a repeating chain.

A word that can be read one way in a certain language and another way in a completely different language.
Mirror ambigram depicting the phrase علي ولي الله (Ali is the vicegerent of God, in Arabic), Ottoman panel, between 1720 and 1730.

A word that can be viewed and interpreted while rotating through multiple different angles.



Mirror and rotational ambigram of an arithmetic operation illustrating the commutative property in addition.

Somewhat like chain ambigrams, but tiled to fill in a 2-dimensional plane
These are just come of the kinds of ambigrams available. I never found an explanation of what people are supposed to use them for, although some of the uses are self-evident.
A FINAL DEFINITION
I noticed some articles which stated that the word Ambigram might not be in the dictionary yet. Doing my due diligence, I looked up the word in Merriam Webster, Dictionary.com, Harper Collins, and the Oxford English Dictionary. It is a dictionary word, although Harper Collins indicates it is still a suggested word for consideration. However, in the process, I also ran onto another definition that isn’t in any of those dictionaries.
Ambigram
"Ambigram is a quinolone/fluoroquinolone antibiotic It is a synthetic fluoroquinolone (fluoroquinolones) with broad-spectrum antibacterial activity against most gram-negative and gram-positive bacteria. Ambigram inhibits bacterial DNA gyrase, which allows the untwisting required to replicate one DNA double helix into two. Notably the drug has 100 times higher affinity for bacterial DNA gyrase than for mammalian.”
JUST SAYIN’ !
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Sources:
https://en.wikipedia.org/wiki/Ambigram
https://ambigramart.com/ambigram-generator/
https://www.pinterest.com/camartica/anagram-ambigram-love/
https://www.adweek.com/creativity/joy-turns-pain-when-you-flip-over-these-clever-suicide-prevention-ads-150621/
https://commons.wikimedia.org/wiki/File:Sator_Square_at_Opp%C3%A8de.jpg
https://commons.wikimedia.org/wiki/File:Ambigram_-_puzzle_-_the_end_-_by_Peter_Newell_1893_-_book_Topsys_and_turvys_(crop).jpg
https://www.yuqo.com/ambigrams-162/#:~:text=An%20ambigram%20is%20an%20artistic%20play%20on%20words,magazines%2C%20albums%2C%20websites%2C%20and%20movies.%20Toggle%20navigation%20Blog
https://www.merriam-webster.com/words-at-play/words-were-watching-ambigram#:~:text=Different%20Meanings%20of%20Ambigram%20The%20most%20common%20use,an%20%27ambigram%2C%27%20designed%20by%20Frank%20Gregory%20of%20Greenfield.