What the Hat?

Helena Fourment, by her husband Peter Paul Rubens, circa 1630 (now on view at The Frick).

I was doing a little research on Peter Paul Rubens’ wife Helena Fourment, this morning. They married in 1630, when he was 53 and she was 16 (ahem), and she inspired some of his most voluptuously and rosy works from then on. (This image was done around the time of their wedding.) As a daughter of a silk merchant from Antwerp, it’s natural that Helena would always be dressed in the latest, but when have you ever, ever, ever seen a hat like this? Does anyone know why our girl is sporting what looks to be a pawn on top of her head? Amazing, right? Google isn’t giving up the goods, so if you can tell me anything about this weird headgear I will be thrilled.