Are you talking about the auto-annotate feature? The D I believe comes more from the GUI and denotes a position diagram. Check out that annotation pages for SCID and you can also check the NAG link on that page.
I'll have to check later on the 30 but I think that may be how many ply; not sure though.
Been expiermenting with this and have some questions about the output results. Went to the stockfish site and wasn't able to find answers.
Example 12...Nd4 + = red D Whait does the red D mean?
30:-0.04 Understand the -0.04 BUT what does the 30: mean?
Lastly stockfish will return results on most moves but not all even though I thought I aksed it to anylize all moves (may need to recheck this).
Any wordds of wisdom??????