A reddish coin bearing the letters MMS is used by the Mors Mortis Society to secretly communicate the time, day, and locations of future meetings to its members.
One such coin was brought to Alexandra Quick by her raven in September 2008. The coin, which Quick noted looked nothing like "either Muggle or Confederation coinage," bore a crudely-stamped bird – either a crow or a raven – on its obverse with the letters MMS beneath the bird's talons, and an empty septagon on its reverse. The back of the coin also featured miniscule writing along its edge, reading: "If this coin be stolen, a Thief's Curse be upon you!"
The coin also changes appearance: the wings of the bird on the front will, within days of a meeting, move like the hands of a clock to indicate a time, while a word appears below the MMS stamp indicating a day, with a further symbol indicating that the time is during either the day or the night. At the same time, a small pinpoint of light will appear within the empty septagon on the back of the coin, indicating the location of the bearer with respect to the layout of the Charmbridge Academy's septagonal lay-out. Within the hour preceding a meeting, a tiny moving arrow will appear on the back of the coin, indicating the direction that the bearer must travel in order to find the meeting location.
This transmutation may be accomplished through the use of the Protean Charm.