Bren,
If you are referring to "juice" in general--you sign a "J" right in
front of the mouth using a double movement.
If you are referring to a certain type of juice you do a single movement
of the "type" of juice and then the sign "drink" using a "C" handshape.
For example, usually the sign "orange" is done using a double movement
as you change from a tight "C" hand into an "S" hand, back to a "C" and
back to an "S." When you do a compound sign however you will note that
the movement of "ORANGE" is reduced to a single change from "C" to "S"
and then continues on into the "DRINK" sign.
It is also permissible to sign "ORANGE" plus "JUICE" (using the "J"
handshape for "juice.")
Grading notes: As an ASL instructor I would not mark a student wrong
for using a "J" handshape. Nor would I mark the student wrong for
using a double movement for the sign ORANGE as part of the compound sign
"ORANGE-JUICE." But some instructors might, so it is always good to
determine how strict your local instructor is regarding various signs.
Additionally, if I were taking an ASL proficiency examination I would
reduce the use of any unnecessary initialization of signs. Which is to
say, I'd do the ORANGE-DRINK version rather than the ORANGE-JUICE
version.
Which brings up an interesting cross-cultural / interpreting issue.
Technically, an "orange drink" is nothing more than orange flavored
sugar water. If it is important to distinguish between actual "juice"
and a "flavored drink" I would clarify by adding the
"real/true/actual/sure" sign to "ORANGE" or by signing "ORANGE PUNCH"
(dominant hand fist striking left index finger). That leads to a
completely different discussion of whether or not the sign "PUNCH" is
appropriate to describe flavored sugar water. As a lexicographer I'm
simply going to state that I often see "PUNCH" being used that way by a
variety of signers and thus it is indeed part of ASL lexicon.