Two days ago the British Museum twitter account posted this item, which seemed to me worthy of wider circulation. They posted a picture of an item in their collection, together with one of the Fayoum mummy portraits depicting it in actual use!
This mystery object is a diadem ornament worn by priests of the god Serapis in Roman Egypt http://ow.ly/THZsg
The juxtaposition is pure genius.
The link goes through to the British Musem site, where bibliography may be found.