I keep seeing this simple border, which looks sort of like a half circle and sort of like a small rectangle, when put through an extruder. It also looks like metal tape/ribbon in the jewelry making section at craft stores. Does anyone know?

It seems to be the same ribbon that is used in the bow around the glass holding the macaroons.
I would just go to your local craft store and check out the ribbon section or even the washi tape section (probably near the scrapbooking area) and see what you can find. Here is a ribon that is similar in the picture...http://www.joann.com/offray-7%2F8inx9-metallic-woven-wired-edge-ribbon-gold/14888382.html. And the reason for the interesting shape is mostly due to the lighting and the fact that the ribbon is attached to a covered cake board so the sides are exactly perfectly straight.
It appears to me to be a gold metalic ribbon attached to the edge of the covered cakeboard with a tiny, extruded straight rope around the bottom which has been painted gold to match the ribbon.
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