Observation can perhaps best be considered as elementary literacy

Observation could be considered as a primitive form of literacy, in which one "reads" the information contained in the environment - in foot-prints [VALL] and tyre-marks [PRIO], in dust [STUD] and ashes [BOSC], in clothes [CREE] and faces [CARD], However, knowing the importance of communication in human affairs, both legitimate and criminal, I have not neglected traditional literacy. Thus, I have explored the typewriter, the use of secret writing, English charters, and the Chaldean roots of the Cornish language, as indicated, respectively, by the following quotations:

It is a curious thing that a typewriter has really quite as much individuality as a man's hand-writing. --- I think of writing another little monograph one of those days on the typewriter and its relation to crime [IDEN].
I am fairly familiar with all forms of secret writings, and am myself the author of a trifling monograph upon the subject, in which I analyze one hundred and sixty separate ciphers [DANC]. Because there are many ciphers which I would read as easily as I do the apocrypha of the agony column - such crude devices amuse the intelligence without fatiguing it [VALL].
Sherlock Holmes was pursuing some laborious researches in early English charters [3STU].
The ancient Cornish language had also arrested his attention, and he had, I remember, conceived the idea that it was akin to the Chaldean, and had been largely derived from the Phoenecian traders in tin [DEVI].