Here is an excellent black and white scan of “Sign of the Four” circa 1917. The cover is scanned in color, but the text was scanned in black and white. It is an excellent scan and the pages are clean and free of marks.
This is definitely written in Pre-Anniversary Shorthand. This is obvious when you look at certain article omissions and shortcuts that were specific to Pre-Anniversary Shorthand.
The plates were written by Alice Rinne Hagar. This book is difficult to read because the proportions of the shorthand characters are out of whack. I have read through it twice, and it is a very challenging read. The plates are much neater than those written by John Gregg. But they are not up to the high standards of Georgie Gregg Gingell and Winifred Kenna Richmond, who created the plates for many of the novels written in Gregg Shorthand that matches the 1916 and 1929 Gregg Manuals. The early novels that match the 1902 Gregg Manual were uncredited and likely created by John Gregg.
There was only one set of Gregg Shorthand plates made for this novel. Gregg continued to sell this book after Anniversary Shorthand was introduced in 1929, but it was never updated to Anniversary Shorthand. Online sellers claim that this book is rare. It seems to be easy to find. Many copies have survived because it was only published in a sturdy hardback edition.