We deal with "design" all the time in archaeology, particularly with things like stone and bone tools.
And there is no way to tell with some items whether they are natural or modified. Creeks and talus slopes can bash or grind items together, sometimes making a natural item appear deliberately modified.
And in fact, some natural items can become artifacts by their use. Good examples are door stops and paper weights. They serve a function, and can be classified as artifacts, but their use doesn't necessarily leave any evidence.
There have been thousands of studies in a variety of fields devoted to determining whether particular items are artifacts, and what their uses were. And there are still items where we just can't tell.
Creationists, on the other hand, are more in the "no study required, I know it when I see it" camp.
Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.