Most of the time I noticed that ASL users tend to spell it.
In French Sign Language, they do sign them:
PISCES: fish
LIBRA: Balance of weight
GEMINI: Twins
AQUARIUS: Carrying a water basket on shoulder and pouring it down
LEO: Lion
SCORPION: the tail stinging
CANCER: French sign for cancer is like chewing down the body with modified C classifiers.
American signs for cancer would be either "C" shaked, or "ACID" or "C chewing down body"
TAURUS: Bull
CAPRICORN: I don't remember the sign for it, though it is half mermaid half goat, right?
SAGITARIUS: act as if you are using an arrow with a bow and letting it go
VIRGO: Virgin
ARIES: I dont remember the french sign for RAM. I dont know ASL sign for it either except to use the classifier for the long reeling horn.