I would argue that one can tell if something is design even if he has no prior knowledge of manufacturing
Depends to what extent you mean that.
Not having knowledge of a certain
type of manufacturing, but having knowledge / experience of
other types of manufacturing, would not necessarily be an obstacle.
Off course, there are objects that are very obviously not natural. Any human from the last 10.000 years would surely recognize instantly that an iphone or a car is not a natural object.
However, humans from as recent as, say, the dark ages would not necessarily recognize a randomly shaped yet intentionally designed carved rock from a naturally occuring one.
Hence why I said that it is a combination of understanding what nature generally can do and being able to recognize signs of manufacturing.
Yes, there are certainly situations that one isn't able to recognize the signs of manufacturing, for a variety of reasons - ignorance being the most obvious one. At that point, one is only left with ones understanding of what nature can and can't do.
Note here how being ignorant of knowing what nature can and can't do, runs the risk of ending in a false positive where one thinks it is designed simply because one does not know how nature might have accomplished it.
This is how we end up with gods throwing lightning bolts, controlling the tides and storms, controlling sunset and sunrise, controlling the volcano's and earthquakes, etc.
Or is this another case where you don’t affirm nor deny anything ?
There really is no need for this party-poopin' passive aggressiveness.
How did the first archeologist of the world who discovered the first carved rock, knew that it was designed? (if he had no prior knowledge on how carved rocks are supposed to look like?
Your hypothetical makes no sense.
Archeologists would know very well how carving would look like. Carving is something humans have been doing ever since homo erectus figured out that stones can be fashioned into cutting tools.
And I just told you above that a person who doesn't know about carving would not be able to tell the difference between a randomly shaped carved rock and a naturally occuring one. And if that is the case, then archeology is not a job that person will be doing.
If an Alien ever finds the Roseta Stone, would he be capable of concluding that the carvings where design?
Depends on the alien.
If the alien is like a cat or a fish: no.
If the alien is an intelligent being so advanced that he managed to travel lightyears across space to get here: yes. That alien will likely instantly realize that it's a written language.