I found a kamabo co poster with an eye symbol on it(the square). There is an ad that has a big eye on it in splatsville ....

Is Tartar literally advertising ?

Is this foreshadowing????

Mr. Grizz knockoff

I believe tartar was advertising, especially in the octarian world, and i imagine that was how it acquired some of its test subjects. There is a kamabo ad in the haikara walker artbook on page 191. none of this is ever made super clear though.

but i really don't think the posters in inkopolis square in s3 are foreshadowing, but the opposite, they look old and torn, i think that's just showing what was there. tartar was destroyed in s2 and side order i think makes that fact clearer since that story is all about the recovery of the sanitized octarians. as for in splatsville, are you sure it's a kamabo co poster? do you have pictures? there's a few signs i can think of in splatsville that feature eyes and arent kamabo. The only kamabo-adjacent thing in s3 i can think of is the sea cucumber phones, with the logo being the same on the CQ cards and text being in deepsea script

but i dont think tartar has anything to do with this since it is Dead, but rather some other company in the deepsea (likely related to CQ Cumber).