Yes, yes -- of course there are many more than just two types of signs.
What that title means is that you can (if you find it helpful) separate signs
into two categories: Expressive signs and receptive signs.
Expressive signs: Signs that you personally use on your own hands.
Receptive Signs: Signs that you do not personally use on your own hands
but that you would recognize if you saw someone else doing that sign.
Older sign language dictionaries and older videos of Deaf people signing are
excellent for "historical research" and for building a "personal mental
signing bank of sign variations that an individual is able to recognize."
When you look in an older sign language dictionary you will probably
notice that many of the signs seem a bit "dated" ("dated" in this situation
means becoming old and not used much lately). Those older signs are still
worth learning even if you don't plan on using them for everyday signing.
By putting those signs in your minds "data bank of signs" you increase your
receptive ASL ability. (That is your ability to watch and understand the signing
of others.) Having a strong receptive vocabulary is particularly important
and good for interpreters.
Having a large knowledge of sign variations is also good for ASL teachers.
Knowing lots of variations helps to reduce the tendency to think "your" way is
the one right way. When a humble ASL teacher sees a version in a
dictionary that is different from their own that instructor doesn't start
pronouncing that the dictionary version is wrong. Instead a humble ASL teacher
makes a mental note that there is at least one dictionary out there (maybe more)
that shows a variation.
Before pronouncing any particular version "wrong," ASL teachers would be well
advised to chill a little and look around a lot to get a feel for why that
version is showing up. Even if you are convinced that a sign is "wrong" it
would be a good idea to use a humble approach when providing feedback to your
students.
Recommended phraseology:
"The way I tend to do it is..."
"The way I see it most in my area is ..."
"I tend to sign it this way..."
Notes: