To expand on what Conder101 said, what I like to do is locate various die markers. Specifically, if any remnant of the last two date digits exist, then I'd match them up with other numerals in the given font (Google the various years to find how the 0-9 numerals look like). Eliminate the digits that it can't be. Combine this with what Conder101 said about the design type, and it may narrow it down considerably - possibly deducting it all the way to what it must be.
As far as the D over S, I can't see anything...usually a good idea to start a new thread with a new question.
