We recently found this when a friend called us asking if this is a possible treasure sign as this was a very old cement which existed during the war and nobody knows it why it was there. As shown from the above picture, it was erected sideways and there is a written numbers and letters then at the middle there is a noticeable arrow pointing downward. The arrow has a small hole nearly at the center and I think this is not just an ordinary PSU land markings. I have heard stories that the Japanese mimics or clones PSU's land markings but they make it differently to avoid confusion and put some of their codes or signs. Then they mix some gold bars or jewelries on to the cement.
This project will be updated soon when we would work it out as we are still saving for another project. Happy treasure hunting everyone. :D