Dr Watson at one point says the American-English word "airplane", whereas in the United Kingdom (where the story is set) the equivalent word is "aeroplane".
When you first see the Rosetta Stone the small sign to the bottom-right of it misspells it as "Roseta Stone". This same shot is repeated towards the end of this episode even though some other shots show the name of the artifact with the correct spelling.
When Moriarty talks to Matt on the cup-phone, when the camera cuts to Matt you can see a noticeable slackness on the cord. Cup- and tin can-phones do not work unless the cord is completely taut so neither character would be able to hear what the other was saying.