Thanks for your analysis. That last letter does look like a "d."
I rule out the possibility of a name in the form Sa##d because this man's family were Scottish Presbyterians who tended to choose their sons' names from a fairly traditional list (e.g., James, John, William, Robert, Thomas, Hugh, Samuel) and I can't think of any name they might use that would look like (or be abbreviated as) S###d. (Siegfried was not among the names they used.)
(I didn't point out the cultural context in my question above because I didn't want other people's analysis of the handwriting to be overly constrained by assumptions about possible names.)