-Ruins of a society with a mish-mash of cultures existing far from their original source
- A ruin far away of a culture that has no recorded history of being there or even visiting
-Gifts from exisiting cultures i.e. phoenicians, egyptians etc to an atlantian king, clearly marked "king of atlantis" or w.e.
(First, I want to be clear that I too am of the opinion that Atlantis was made up entirely by Plato)
The first two do not implicate Atlantis. However, I could see the discoverers associating them with Atlantis if they are located in the place where those discoverers think Atlantis is at the time of discovery.
Whether the discoverers would recognize this as Atlantis would entirely depend on when the discovery happened. Egyptian writing was not translated by modern civilization until the early nineteenth century. Even then, assuming hieroglyphics were used, as there were generally no vowels, the most you would be able to translate was something like "tlnts". I believe phoenician was similar.
Even then, there're some other problems. I believe Plato said that Atlantis had sunk about 9,000 years before Solon, which would make it 9600 B.C..
The earliest writing system known to modern times, Sumerian, has only been dated back to about 3500 B.C.
If, for some odd reason, there was some known writing system going back that early that could be translated phonetically, there's a lot of time for linguistic drift between that gift and Plato's account, which would probably make the name on that gift almost unrecognizable. Remember that translating a possible Atlantean writing system would be almost impossible as we would have no idea what Altantean language sounded like, unless there was something like a rosetta stone to help.
Of course, Plato may be "wrong" about that date, which, of course, means that he might have been wrong about any other part of the story, including the name. In which case, there is almost no way to connect some ancient civilization to Atlantis -- any ruins found would at most simply get appended to the already long list of civilizations mentioned above which "might" be Atlantis.