Dear Khun Sanya,
Since I just received the new information that the size of signboard is not more than 3 square meter hence OTH may not have to pay for the tax.
However, The government officer said that they will visit to Olympus to check about the house and land tax, (the building owner shall be responsible for the house and land tax) and they may check the size of signboard again therefore I will not prepare documents for submit to officer. (please inform me if the officer ask OTH to pay for the tax)
should you have any questions, please feel free to let me know.