Strange symbol on architecture plan

So out within the yard I discovered this factor buried a few foot beneath the floor. My home was inbuilt 1992. The panorama plan was drawn in 1998 when the home was offered. This image corresponds to no matter is buried on the market, however it’s so blurry I can’t make out the 2 phrases beneath it. I’m aware of engineering plans however have by no means seen this image. I’m questioning if the unique proprietor buried a time capsule. The sq. prime seems to be a lid and seems to be steel. It’s set in a concrete cylinder. Any concepts on what this is likely to be or what these two phrases are? The unique proprietor is deceased and I’ve not been capable of finding any descendants to ask.