"A23T" for some reason is ringing in my head as a type or font management somethingorother. That file is no doubt either a registration or preference file. Knowing the contents of the file may be helpful in identifying it. Were you able to find it? It should be immune to spotlight, but you can use the terminal FIND command probably.
find ~ -name ".a23t.mk4e.plist"
though it's very likely to be in your ~/Library/Preferences/ someplace with an extension like "plist".
If that doesn't find it, try
find / -name ".a23t.mk4e.plist"
Once you find it, tell is where it was, what its creation / modification dates are, and show us a snippet of its contents:
stat (type path here)
and
cat (type path here) | xxd -c 32 | head -n 20
