Yes that is the point, one can recognize design in a thing even if you don’t have prior evidence for the existence of the designer.
Do you grant this point?
Not as written. You missed crucial information.
Like "signs of manufacturing", which we recognize through our own experience with manufacturing.
That, and our knowledge of natural processes, is how we distinguish between artificially manufactured things and natural occurrences.
So, to repeat: we can recognize design in certain things because:
1. we have a rather good idea of what nature can and can not do (yet there are still unknowns)
2. we understand the process of manufacturing and are able to use that experience and knowledge to recognize signs of manufacturing in certain objects.
It's, for example, how we can distinguish an artificially carved rock from a naturally eroded rock.
Because we understand and know how the results of erosion look like
And we understand and know how the results of carving look like.
So even if we deal with a seemingly randomly shaped rock with no particular function... then still we would be able to tell if it got its shape from carving or not. And we'ld recgonize it simply because it would have traces of carving.
Each manufacturing technique leaves its marks. Then there's also the used materials and the way they are put together (glue, bolts, nails, screws, etc).