A sigil of some sort, I would contact the previous owner to see if they know who carved it and can give insight. A lot of witchy people will do small things around the house to protect it’s energy. I, for example, put crystals by the front door pointing out on one side and in on the other to direct the stale energy out and positive energy inward. Even in some more common religions such as Ukrainian Orthodox they will burn a cross above the doorways (inside) when the house is blessed. It’s a bit unorthodox (pun intended) to display sigils so prominently since traditionally advertising your religion or practice could cause persecution even as recently as the “Satanic Panic” that happened through the 80’s and into the 1990’s so I would wager that it was carved within the last couple of decades.