> I have a hypothesis, which incorporates the fact that the Dogon were not reported to have such knowledge until the 1930s, well after the discovery of Sirius B.

That's not a fact, because there are several sources / individuals that dispute this claim.

> A bit of searching is coming up short, beyond a claim about shackles on the ankles of a Roman statue of Saturn (the god) symbolizing the rings; I find this less convincing than the idea that they symbolize shackles (the ones with which he was bound in Tartaros).

Well you're pretty terrible at searching the internet then, considering I can type Sumerian saturn symbolism into any image search engine and find a plethora of examples.