Fun factoid: Chips need to have patterns, even where there is nothing to print! This is because you want the acid etchant to be consumed the same way everywhere. So you choose a random repeating pattern that has the same density as your other signals density; it will serves no purpose other than consuming nitric acid. But you have freedom in choosing the exact shape.

Source: a friend of mine working at a chip company 20 years ago. They considered disparaging the competition billions of time in tiny 250nm letters. It occurred right after a patent dispute where it was highly likely they had reverse-engineered part of their design. A disdainful message only their competitor would read, to the tune of "we know you're cheating, and fart in your general direction". It was mostly a joke though, they did not go through with it.

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AMD's one is only in one corner of the chip, so I don't think it applies here.

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EDIT: this was a long time ago. Seems like filling has evolved quite a lot [1]. Timing, signal integrity, and probably capacitance too are so constrained nowadays you can no longer write a personalized message to your competitors.

[1] https://semiengineering.com/knowledge_centers/materials/fill...