Ok, one way to tell is....Only works with completed game i think.
Look in the folder for the version you played in My Games, look in the Metaverse folder.
For my last completed game it was DA so my path is,
You should find a XML file in there that corresponds to your game in question. If not than you may well have started a sandbox game. The XML file will have a name that has the date of completion and about 9 other numbers...
20090210123456789.XML, something like that.
It will list the character you played with, the score, the difficaulty level (represented by a number 11 is suicidal), galaxy size and even your serial, so dont post that file in here.
If you don't find that file, provided you have not deleted that folder for whatever reason, then i'd say it was not a MV game. Look then in the SandboxGames folder and see if there is a corresponding XML for that game in there.
This is still not the file i was talking about but should tell you all the same.