Some of the symbols (e.g. /) are included between the letters such as b/c for because, w/ for with and w/o for without.
Some abbreviations are based on the first and last letter, for example wd for word, ht for height, wt for weight, or are based only on some consonants, such as mgt for management.
Many symbols are international ones, such as
+ for plus,
& for and,
# for number,
! for important,
= for is/equals,
< for less than,
> for greater than,
? for confused.