In a fragment of a small glass flask (?), we see two faces staring at us. It is the Roman god Janus. Janus is the god of gates, doors, doorways, beginnings and endings. His most prominent remnant in modern culture is his namesake, the month of January, which begins the new year. He is most often depicted as having two faces or heads, facing in opposite directions. These heads were rumored to look both into the future and the past.
Our Janus is somewhat hard to see in this photo. One face is looking to the left: