TBM

When I saw this in the pavement I thought it a candidate for CanCarrier's 'embedded' series, 'til Mr Flum told me what it was; then I nabbed it for a blip of my own.
The small 'button' within the yellow triangle is a Temporary Bench Mark, left by a surveyor when working on the street and the letters MAG on the head refer to the manufacturer, Magnail. Apparently this is the nail of choice for the purpose.

I have begun backblipping our break in Suffolk, starting here.