Possible Lincoln artifact discovered!

[Eva Elisabeth]

The evidence, thus far, DO point to our dear Tad.

What evidence, please? (This is a serious question!)
What about this having been the mark of a carpenter named Theodore Adam Davis? And I'd think there were quite some people nicknamed Tad (and his actual name was Thomas, not Tad).
BTW, now you seem to date the carving to sometime between 1840 - 1860, at least that's how I read your latest post.

One factor that makes me think of a trademark first is that the letters are in print. Even in my school days we only learned to write cursive.