It originated in the bluming times of timber framing in europe,way before America was discovered, and still is used today.
All timbers in a wall are numbered continuesly with roman numbers. ( I, II, III, IV etc.)This # is always on the left or bottom side of the timber.

All walls (gutter walls or walls length side with the house) get a " /" (dash ;1st wall : / 2nd: // 3rd wall : ///) behind the roman #

All gable walls get a nodge in the number. The 1st gable wall has one nodge, 2nd two etc.

First floor has only the numbers on the timber, 2nd gets a triangle behind the dash or the roman number with the nodge.3rd floor gets two triangles etc.

If there would be more walls across they could be marked with a square.

All marks should be carved in across the grain.