It’s a marker for a buried gas pipeline. Arrow points to where the gas heads to. The marker is used to easily identify which areas need to be dug up, in case maintenance (e.g. pipe replacement) is needed, or to avoid the pipes during excavation work.
Reference (in Japanese):
http://www.yotsugi.co.jp/products/detail/233
Credit:stackoverflow.com‘
4 Mar, 2024
5 Mar, 2024