I include a copyright notice at the bottom of these freely available pdf files because I do want people to know where they came from. If that notice really bugs you, you can email me for the tex files. I've noticed other work I've posted online (notes, master's thesis, etc.) showing up all over the place, probably aggregated and copied by robots, and when that happens attribution doesn't always occur.
Feel free, though, to modify these activities and use them for any sort of educational purpose! If you like something but need to rewrite it for pedagogical purposes, go for it.