It may or may not be fine, but my guess is that calling your Zazzle shop y-combinator is a bit much. Yes it's a generic term, but out of courtesy you should probably rename it to something like pgfan or something that indicates that you're not somehow "official"...
This is actually the "Tagxedo" shop in Zazzle, and the category is called "Y Combinator".
The link goes to http://www.tagxedo.com/shop/y-combinator so this is also Tagxedo shop Y Combinator category. It's clearly stated that this is a tribute. I don't think I used language that is misleading, but I'll triple check.
