That's a D-ring. We've had trouble getting them, so we went to O-rings. We loop a piece of nylon webbing through the ring, fold the hem over it, and then sew it into the hem (usually making an additional "X" for added strength). We used to sew webbing in all the hems for street banners, but we found it was hard for the client to store them and wasn't really necessary anyway. We recommend O-rings if the banner will be hung between posts with bungee cords. The cords keep the banner taut to prevent sagging. And unlike grommets, it's almost impossible to pull out. We get O-rings and webbing from Fellers (it's not in their catalogs), but there are other sources. We use a Consew 225 sewing machine--they are damn near bullet-proof (single stitch).
Quick Stitch in Lombard, IL, will sew banners. Great to work with and fast.