Both China and Iran have character styles that are characterized by being (at least approximately) based on a square raster and by "filling up the plane" in the sense that if you take any 2x2 squares from that raster, at least one square will be background and at least one square will not.
In Iran, such writing is often seen on mosques:
(I have marked the word "Allah"/الله)
but it also appears on the national flag:
(this apparently reads "Allahu akbar"/الله أكبر (+ one repetition))
This character style is apparently called "Square kufic" and wikipedia has some more beautiful examples.
In China, a similar character style is used on seals. These ones appear on a 12th century copy of the famous painting "The night revels of Han Xizai":
And this one on the similarly famous 12th century painting "Along the river during the Qingming festival":
Now China and Iran are quite distant, which would make it seem as if these writing styles must have emerged independently from each other. However, there actually is an instance where these blocky Chinese seals and blocky Persian/Arabic religious inscriptions were used in the same place at the same time: In Ilkhanid Iran, in the late 13th/ early 14th centuries.
At that time, both Iran and China were ruled by Mongols, and the Mongol rulers in Iran (the Ilkhans) found it politically expedient to recognize the Mongol rulers in China (the Yuan dynasty) as their overlords. For this reason, they received seals from China, and they apparently also made up some Chinese-language seals themselves. Below are seals of the Ilkhans Öljeitü (image source with transcription of the seal, note that the direction of writing seems to vertical and then from right to left) and Ghazan (image source with transcription of the seal, ditto about writing direction):
Öljeitü (the one with the red seal above) had a large mausoleum built for himself which stands to this day, and which houses several square Kufi inscriptions, both inside and, quite prominently, on the outside (image source):
Given the formal similarities between these character styles, I have wondered if these writing styles are related, or if maybe at least one clearly precedes the other. The wikipedia article on Kufic scripts (also linked to above) says the Iranian writing style dates from the 12th century. The Chinese examples I found are on paintings from the 12th century, but I can neither rule out that there are earlier examples, nor that these seals were only added later. Unfortunately the only articles on the Chinese styles that I found were somewhat unspecific.