From the Wikipedia page [1]

A Book from the Sky (simplified Chinese: 天书; traditional Chinese: 天書; pinyin: Tiānshū) is the title of a book produced by Chinese artist Xu Bing in the style of fine editions from the Song and Ming dynasties, but filled entirely with meaningless glyphs designed to resemble traditional Chinese characters.[1] The book, which consists of four volumes totaling 604 pages, was printed in a single print run of 126 copies between 1987 and 1991,[2]:61 and was first publicly exhibited in October 1988, in Beijing's China Art Gallery.[3]

The work was originally titled Mirror to Analyze the World: The Century’s Final Volume (simplified Chinese: 析世鉴-世纪末卷; traditional Chinese: 析世鍳-世紀末卷; pinyin: Xī shì jiàn—Shìjì mòjuǎn), a title which “evokes the trope of the book as jian 鍳 or mirror in the venerable tradition of imperial historiography”. However, the artist eventually felt that this title was “cumbersome” and “heavily influenced by Western forms and the current cultural climate”, and decided to adopt the name that was already in popular use, Tiānshū. In Chinese, the term tiān shū (“divine writing”) originally referred to certain kinds of religious texts, but is now used to mean “gibberish”; it has thus been suggested that Nonsense Writing would be a more appropriate translation of the title.

The Chinese idiomatic expression "天書" (celestial script) is a metaphor for incomprehensible writing somewhat akin to "chicken scratch" in English, referring to a writing system of unknown origins never seen before by mankind

Later versions of these characters incorporated English letters into square word-shapes, which he called Square Word Calligraphy.