Hi D and all,
Let's approach the question logically, shall we? First of all US callsigns begin with the letters A, K, N and W and A and N may be tossed out because they have only been assigned to a particualr series of Amateur calls. That leaves W and K, only the second and possibly a third letter is missing. Now we run a geosearch by frequency in the area a in question and the odds are in favor of only one matching what you already have. The field of choice will be narrow, there can't be more than a few transmitters on any given frequency within 50 miles or so of any given center point and usually they're spaced at least 20 miles apart.
Just for future reference, the maximum code speed allowed is 20WPM and many who set up repeater controllers push it to the wall. It's not easy to read by less than an experienced CW operator so recording it and playing it back over and over will help you separate the characters if you concentrate on them one by one. A much better trick is using a good digital editor to slow it down to a speed you can copy more easily and still you can loop it and pick out the characters one by one.
If all else fails use an Edison pen recorder but you'll have to get a book from the library and build it yourself. (;->) Hey, I'm being facetious, but there is the modern version. Many freeware Amateur Radio digital coder/decoder programs can copy and send CW so you can use one to read the code. I use MixW2 which has a pretty fair CW function even if my favorite mode is BPSK31. Now don't ask me where to download the program. Google is your friend, I'm not!
Oh Mick, I can't seem to find the +F key. I had the same trouble when the panel popped up saying "To start press any key." and I couldn't find the any key. Are we looking at a Cyrillic keyboard here?