It does look like a horseman, but it is going the wrong way. I have only seen one other example of a horseman leaping left, out of many dozens of examples...and these were all from officina B. The engraving of the shield is also fairly crude. The altar on the reverse should also have an S on it for workshop gamma, which this one may, but I am not completely sure. This could be an unofficial issue...but it seems most likely official.
