For along,long time there was no marking of any kind on any restoration.
Then he started offering a small % discount to the customer that 'allowed' the DT marking stamped inconspicuously.
Parkers were by far the biggest restoration job then and the mark was placed down in the dolls head cut in the frame on them.
Shockingly most customers never wanted any such marking on their gun no matter the mfg'r..
The Parker placement of the mark makes for easy removal anyway.
Upgrades done on speculation, presented and sold as such were sometimes prominently marked w/the stamping.
I don't know what they do there now.