In regard to foreshadowing in "The Tell Tale Heart", I think he makes it clear from page one where he is going. Specifically, in the second paragraph: "It is impossible to say.....and thus rid myself of the eye forever." He clearly establishes his mission here. And if that doesn't do it for you, how about the the line in the next paragraph where he states. "I was never kinder to the old man than during the whole week before I killed him." If my understanding of foreshadowing is correct (a sign or indicator of something to come), then I don't think there were any more definitive indicators than these. Of course, if you're concerned with his state of mind, the very first paragraph "foreshadows" the mindset of the narrator.
Hope it helps! :) It's an awesome poem XD