Mike you might be able to make a semi-educated guess as to the mode by comparing your recording to known recordings of digital signals. This wiki article has several links for this purpose...
HF Digital Decoding - The RadioReference Wiki
Many folks who fool around on digital also have the capability to view the audio waveform - it's not 100% accurate, of course, since local conditions and the receiver might introduce unwanted traces, but it's another tool that people can use. Many packages have the ability to generate the waveform just by feeding the audio into your PC and letting software do the work. MixW can do this, and I'm sure there are a great many others.
Although a lot of these type of packages are ham-related, don't ignore their potential usefullness in being a detective...best regards..Mike