I have just done a test recording of a programme with 5.1 ch audio, and can confirm that there is no indication on the i-plate, or front panel, that the programme is 5.1 ch or stereo.
Also, as far as I'm aware, the Dolby Digital and Dolby Digital Plus icons have never, nor will ever be used, as the box does not receive Dolby Digital signals, it simply transcodes the received signal to output the Dolby signal that can be recognised by an AV amp, or suitable TV.
As Graham mentioned earlier, when connected to an AV amp, this should indicate the presence of a Dolby Digital 5.1 ch programme.