Hold your hands together as if representing a book. Open your hands
(as if showing a book opening. Bend your hands at the large
knuckles, fingers straight, the pad of your thumb touching near the
pad of your middle finger (as if holding a shirt in front of you).
Pivot your hands forward (your arms do not move, the movement is in
your wrist). Do it all in one smooth motion.
"How many bookstores are there in this city?"
= THIS CITY, BOOKSTORE, HOW-MANY?
"Bookstore" is a compound word. It is also a compound sign.
The sign "BOOK" normally uses a double movement.
The sign "STORE" normally uses a double movement.
When you combine the two signs into a compound sign you drop one
of the movements of BOOK and one of the movements of STORE.
Sure, you will see people doing variations. You will see some
people doing the full sign for book and the full sign for store and
combining them to mean bookstore. But what I'm telling you is that
is a waste of time and effort.
When you do this sign
using just a single movement normally it would be mean an "open
book" (or "the book was open").
When done as a separate sign, the sign STORE uses a double movement.
If you use a single movement it tends to mean the verb "SELL."
So, really, what we are doing is we are combining the signs
"open-BOOK" and "SELL" to mean BOOKSTORE.
Remember though, do it however your local instructor or Deaf friends