Alchemical, astrological, and medical-chemical (chemiatric) texts are notoriously difficult and often made completely inaccessible through interlarding with "occult" ciphers. These are "sigils" that are neither abbreviations nor hieroglyphic symbols, but belong to a category of their own. They were probably meant to exclude the profane reader or else to place on record an imagined discovery or new recipe for transmutation without giving the secret away. Some of the sigils are consistent and what they stand for has been known for a long time in a well-established tradition. However, there are innumerable variants and problems of deciphering that remain.
A historical and graphical basis of the sigils can be found in various archetypal alphabets, notably those related to ancient Hebrew scripts and the extant "secret" alphabets that are derived from them.
It falls into two main parts, first the Lexicon proper with its 1500 subject-entries and pictographs in alphabetical order, and second an index of sigils for their identification by counting strokes (1-5) and recognizing curvings and additional circles. (from the review by Walter Pagel)
2 pages from this book :
A late fifteenth century selection of sigils from Agrippa 1531
Link to download it :