[Fester Chugabrew]

We identify objects of unknown origin as man-made by comparing them with other objects of known origin--man-made and naturally ocurring.

I can understand how comparisons are of value in determining the presence of intelligent design or not. What I am asking is, when the comparisions are made, what attributes of the object lead to the observer to a conclusion?

[Condorman]

What I am asking is, when the comparisions are made, what attributes of the object lead to the observer to a conclusion?

It depends entirely on the objects in question. And with respect to living organisms, I don't claim that any wild specimen was designed.