Kat, check out all the photos of this recently finished auction. The seller is reputable, so this is a real vessel:
Hohokam Pottery Sacaton Red on Buff Seedpod Effigy Prehistoric Anasazi | eBay
The seller supplies a link to his virtual SW pottery museum(highly recommended, BTW), where you can scroll down and see the same vessel as the one being sold. There, you find the following description:
".....It has been written that these knobbed vessels may represent Datura seed pods, a plant that contained medicinal and hallucinogenic properties. I propose another possibility, the red fruit of the prickly pear cactus. The meat of this fruit is wonderfully sweet and delicious, it can be dried, and it was likely that the Native Americans anxiously awaited the annual harvest of these sugary treats. Prickly Pear Cactus today grow in abundance in areas of the southwest and the fruit is made into jellies and candies."
I'll take you right to the description page. You'll find the vessel way down this page, just a tiny photo there. Think it's a very good chance you found something along these lines. Does not have to be Hohokam, probably a shared design, but I'm not certain. Hohokam ware would have been traded far and wide anyway...
http://www.rarepottery.info/protect/hohokamsacaton.htm
Here ya go, straight to this page gives you a good idea. You may have some version of this SW style. I knew I had seen it before, just didn't know where. That is a great site for SW pottery photos and ID.
http://www.rarepottery.info/protect/hohokamvariantsacatonredonbuff.htm
i stumbled across this completely by chance a little while ago, checking completed Hohokam auctions on eBay as I buy some from time to time.
Of all the SW cultures, the Hohokam felt the most influence from the Mesoamerican civilizations to their south, particularly western Mexico, as opposed to the Maya. But this design is not necessarily borrowed from the south, I don't know the answer to that. But this type of seed pod effigy is an interesting possible answer to your puzzle sherd.