Notes:

1. Short, flat, top section
2. Diagonal edge, from lower left to upper right.
3. Edge. Note that it is not parallel with the edge in note 2. Note that included angle formed with edge 2 is approximately 45 degrees.
4. Layer on top of lower portion of symbol #15, fully obscuring the lower portion of the symbol.

Note the narrowness of the top of the symbol, and specifically the angularity, and absence of curvature, or loops.

A 0 needs wide curvature at the top of the symbol. There is support for neither. This excludes a 0.

A 2 needs wide curvature at the top of the symbol, and an opening to the upper left of an upper loop. There is no support for this. This excludes a 2.

A 3 needs wide curvature at the top of the symbol, and an opening to the upper left of an upper loop. There is no support for this. This excludes a 3.

An 8 needs a loop at the top of the symbol. There is no support for this. This excludes an 8.

A 9 needs a loop at the top of the symbol. There is no support for this. This excludes a 9.

The initial candidates for symbol #15 are 1, 4, 5, 6 and 7.

The width of the top of the symbol is too narrow to support a 7. Further, the diagonal of the symbol is connected to the upper left of the symbol and not the upper right as would be required for a 7. There is insufficient support for a 7 and it is therefore removed from the symbol candidate list.

The edge located at note 3 is inconsistent with a 5, further the width of the top of the symbol is too narrow to support a 5. There is insufficient support for a 5 and it is therefore removed from the symbol candidate list.
There is inadequate curvature at the top of the symbol to support a 6. Further, the 45 degree included angle between the edges 2 and 3 conflict with the features required for a 6. There is insufficient support for a 6 and it is therefore removed from the symbol candidate list.

The narrow width of the top of the symbol supports a 1, however the 45 degree included angle between edges 2 and 3 conflict with the features required for a 1. There is insufficient support for a 1 and it is therefore removed from the candidate list.

The narrow width of the top of the symbol supports a 4, and the 45 degree included angle between edges 2 and 3 are consistent with the features required for a 4.

Outline: The yellow overlay is the visible portion of the symbol’s outline. This overlay is the partial outline for a “4” which is supported by the evidence.

Conclusion: The symbol features suggest TIGHAR artifact 2-6-S-45 symbol #15 is probably a four (“4”). The most likely first alternate is a one “1.”

Summary: Assuming there are 7 digits in the presumed patent number on 2-6-S-45. The current most likely set of digits are 1,894,_ _ _ (where “_” represents a digit yet to be determined).