Thanks, RoninB4. I should've stopped at, "...organic to Klein and mean something else," or stayed more vague, such as "...organic to Klein and mean something else to the manufacturing process." My use of the term "die code" in this case was just to refer to a generic manufacturing code, made with a die, that we typically find on plier handles or wrenches, etc. from other mfgrs.
Whatever the symbols are meant to signify, there are several different ones, they always appear in front of the date code, they are extraneous to the date code, they appear during both date code systems (the early numeric M-YY format, and the later MKLEINCORP QYY format), and, they have never been explained by Klein or anyone else.
Since you worked at the plant, albeit in the tool room, not on the floor, maybe you could offer some potential possibilities.
If you scroll through the photos in the thread, you will see the following:
0-4-37, where the "4-37" signifies April 1937, and the "0" is one of the unexplained codes
2 4-27, where the "4-27" signifies April 1927, and the "2" is one of the unexplained codes
/_\ KER, where the "K E R" signifies 2nd Qtr 1949, and the delta symbol is one of the unexplained codes
O LER, where the "L E R" signifies 3rd Qtr 1949, and another unexplained "O" symbol/code
X EEK, where the "E E K" signifies 4th Qtr 1942, and the "X" symbol is one of the unexplained codes
O-L-EK, where the "L-EK" signifies 3rd Qtr 1942, and another unexplained "O" symbol/code again
O-E-EC, where the "E-EC" signifies 4th Qtr 1947, and another unexplained "O" symbol/code again
/_\ MNE, where the "MNE" signifies 1st Qtr 1964, and another unexplained delta symbol/code
/_\ EII, where the "EII" signifies 4th Qtr 1955, and another unexplained delta symbol/code
EDIT: If someone more adept than me knows how to make an actual delta symbol, please let me know and I will edit my post.