I would label it an optimization process

Evolution is an optimization process, but it doesn't have "purpose" - it simply has byproducts that appear purposeful to humans.

Really, most of your comment just helps illustrate my point that purposefulness is a label attached by the observer: your knowledge (or lack thereof) of Martians is not something that changes the nature of the rock pattern itself, not even if you observe the Martian placing the rocks.

(In fact, your intiial estimate of whether the Martian's behavior is purposeful is going to depend largely on a bunch of hardwired sensory heuristics. If the Martian moves a lot slower than typical Earth wildlife, for example, you're less likely to notice it as a candidate for purposeful behavior in the first place.)