I googled, but I couldn't find it anywhere. It's a rhombus with hebrew inscriptions that look like [dots meant as space]:
...S n W n ...7
Since I found it, I'm curious to its meaning. This little symbolic metal piece (made of antimony, about 8 to 9 centimetres) was left on the door of the direction of the jewish company on the top floor of my father's building when they moved away from it after more than ten years in locus.
It will probably help if you wish to see my sketch: