One of the examples of foreshadowing in "The Adventure of the Speckled Band" - would be the last words of Helen Stoner's sister, Julia: "The speckled band!" right before Julia died, and to be exact - murdered. By creating a mystery around these words, author foreshadows the mystery Holmes has to unravel in the story.
Another examples would be mentioning that Roylott, Helen's stepfather, while in India, was imprisoned for murdering his butler, foreshadowing Roylott's murderous nature. Also, mentioning Roylott's fascination with deadly, exotic animals, foreshadows the murder weapon.
I can not give you the exact page , because it would depend on the edition, - if you refer me to the book you use, I will tell you the exact page. This is a small story and it should be fairly easy to find the page(s).