Consider this the first stab at formalizing a system, or at least my system, for marking the ends of lumber with key information to help with organizing, identifying and selection. 

Backstory

When I had moved into my Baltimore Shop (as detailed in the A Shop of My Own article) there was a very limited amount of space. As a result, lumber had to be stored horizontally on wall racks to give clearance to the machines. This was not ideal; I realized immediately how important it was to store wood vertically, short in front, tall in back. In that arrangement one could quickly see grain, estimate length and width, and usually identify species.

With the lumber horizontal, all I could see was edges, and often only those that were at the front of the pile. There needed to be a system to mark the ends of boards so I could know all the details of the piece at a glance. By formalizing this system, I could reference this article when I inevitably forget what my own markings mean. Surprisingly, extensive google searching yielded few results for other systems to consider. What follows is a "first stab" that I hope to refine a little with feedback from other woodworkers. 

Summary

Wood to be marked on ground end with symbols indicating following information. Ideally boards will be stacked in order of flitch cut, the top of a board being the skyward side when on the mill. 

If rough cutting, mark before end seal if possible. Marks are in priority order, so lower priority marks can be eliminated due to lack of space. Write all marks with black permanent marker or silver paint pen depending on wood color.

1. Species
2. Tree Orientation
3. Flitch Position
4. Date Cut
5. Grain Direction
6. Face Defects
7. Thickness
8. Length

Species

Species codes assembled from those listed here and here. The code list below is canonical, adaptations to the linked lists made for common name compatibility.  Code placed on upper left corner of board.

Tree Orientation

If known place a small stylized arrow in the top right corner of the board indicating direction of North as well as basic geography indicator, noting placement of try on major features, mountain, plain, etc.

Flitch Position

In flitch stacks indicate position with a number within a circle, under the species mark. Number indicates position and/or order of cut. For example, a fully flat sawn log will have numbers ascending from the top of the stack to the bottom.

Date Cut

Under the flitch position list month and year cut in the format "6-17" using a dash so as not to confuse with thickness markings. If the date cut is unknown because the wood was purchased, use the marking P instead of the date. P followed by a date would indicate the wood was puchased on that date, rather than cut.

Grain Direction

A long line with major grain direction, on the left side of the board, under the position marks. Redundant in some cases but helpful for quick identification from far away.

Face Defects

Along eatch edge of the board indicate if there are any face defects with a dot, two dots for generally knotty and a short line for clear.

Thickness and Length

In center of board indicate thickness as a nominal quarter value and measured, indicate length in inches, separate with an x. For example: 4/4x120 or 8/4x96.