The numbers before the letter is the microfilm number.
The D means it is a death record. The number after the D is the page where the information was found. The information found on the foregoing microfilm location will appear after the number. If an entry has just the letter and page number then refer to the previous microfilm number.
A code such as 93CF451 means 1893 census family 451. Since there is no film number preceding the census year, refer to the previous film number.
ANOTHER EXAMPLE: 0573850C97IN1411.
0573850 is the microfilm number.
C97 is the 1897 census.
IN1411 means individual number 1411 on the census.
A series of letters and numbers such as C89,C90,C92 shows the person appears on these three records but no new information was found.
A# or A#s indicates allotment number or numbers found on this page and entered on record.
A (/) indicates the end of the information from the previous film or page number.