I couldn't find an image of an O/U Charles Daly by Richard Schüler / August Schüler Herkules(1910) action with the stamp of a pick and ore tub in the shape of a foot but I did find a Mahrholdt Hakenloser Herkules Bockgewehr with the stamp on the underside of the lumpless tubes on page 74 of the Double Gun Journal Winter 1998/Vol. 9 Issue 4. I find it difficult to believe that either Richard Mahrholdt of Innsbruck or August Schüler made the examples but sourced them. And the source will reveal the maker behind the stamp.