Now you do...
Unknown.[1] Earliest attestation in 1863 US, specifically Texas.[1] A theory is that it comes from the brass tacks in the counter of a hardware store or draper’s shop used to measure cloth in precise units (rather than holding one end to the nose and stretching out the arm to approximately one yard). Another possibility is the 19th century American practice of using brass tacks to spell out the initials of the deceased on the top of their coffin.
Cool thanks.