The lack of flakes or marks does not mean this is not man made. Catlinite effigies are perfect examples. Many native stone tools and adornments are ground. As for this I don't know without seeing more angles or knowing if it comes from a confirmed NA site. If it was just found at random with no nearby native stuff I would say probably not. If it was found near NA stuff I would say a solid maybe. If it was catlinite I would say probably.
I have doubts (a lot) but the round humps have me interested in seeing more pictures. Would like more context of where found. Every time I see title effigy always skeptical but shape is odd. I def would have picked this up if at a site to ask for second looks. Like to see if any marks around edges of the humps
I would have liked to see the interior surfaces of the indentations as well. How can I know if those indentations have not been pecked and ground in if I can't even see them?? Sure it's likely natural, but I've been collecting for 60 years and I have found many rudimentary waterworn notched weights because I picked up a "possibility" and was able to detect pecking in or around the notches even though waterworn. Of course this is not a notched weight nor a squirrel effigy. But I would have picked it up to more closely examine the notches, which, again, do not show their interior surfaces in these photos. And I don't think I would need to take up stamp collecting just because I wanted to satisfy my curiosity....
look at it this way...if someone took the great amount of time to fashion that stone, with all the pecking, grinding and smoothing....they would have taken the short amount of extra time to make it obvious as an effigy.