It turns out. it's not real. A quote falsely attributed to the Minnesota Planetarium Society suggests that there is a 13th Zodiac sign, “Ophiuchus” that appears between Scorpio and Sagittarius that would result in bumping everyone’s Zodiac signs over by a month.
What actually happened is that the Minneapolis Star Tribune a interviewed member of the society’s board, who merely pointed out that our Zodiac system is technically wrong. The Zodiac symbols are all named after constellations that can be seen from earth. However, over thousands of years, the Earth has shifted on its axis. This means that the year represented by a particular Zodiac sign is no longer the best time to see the corresponding constellation. Thus “"When [astrologers] say that the sun is in Pisces, it's really not in Pisces,"”
This has actually been the case for a long time, but there’s been no push to correct the Zodiac calendar to match up with astronomical reality.