Josh,
Sorry, not a chastise and I haven't a clue what your age is. I simply misunderstood your question. Because The D&S was a private co. means their company records aren't open to public scrutiny. If the script they chose was common then I suppose you would have found your answer. But I suspect D&S conscripted someone with an artistic bent to design their logo lettering and associated artwork. A draftsman would be obligated to use common fonts of the era, whereas artists have free reign to come-up with anything that pleases the customer. This discussion reminds me of the question, "How did Roman become Railroad?"
George