Discerning Watermarks: The 1914 Wash-Franks

Having obtained a set of Scott U.S. 424-440, I'm doing my best to determine the veracity of each stamp's identity. I understand that this series is perf 10 with a single-line watermark. As you will see below from sample images of this set (wet & dry side-by-side), watermarks can be inscrutable. Comments are welcome.

ONE CENT. There appears to be a serif "S" appearing on the upper half, perched right on the center point of the stamp. Note the (mistaken?) pencil annotation "462" from days past, which if true, would be indicated by a lack of watermark:


FOUR CENTS. This is problematic. There MAY be a portion of a large, upside-down "U" in the lower left corner:


FIVE CENTS. The upside-down sans-serif "U" removes all doubt here:


NINE CENTS: Looks like a serif "S" perched on Ben's collarbone. Probably okay.


TEN CENTS. Totally inconclusive.


Thanks in advance.

The four cent has an S in the top left corner. Watermarks on orange or yellow stamps like the 10 cent are almost always the most difficult to see. Might be a "U" in the top right corner.