Since David was evidently too modest to mention his own work, I should
point out:

… which also has more analysis of other sign writing systems.

Just on the political side of things: yes, American Deaf culture is a
bit insular. But in fairness there are good reasons. ASL was for a
long time considered not even a language at all, and even to this day
is often suppressed in classrooms by oralists (who believe that
learning a sign language will only retard a deaf child's ability to
learn to speak and read lips, the only forms of language they think
are adequate to get by IRL). Gallaudet, the biggest Deaf university,
was run primarily by hearing people up until just a few years ago.
It's a culture that's had active attempts to suppress its language and
has a legitimate problem with being cast as second class citizens even
within their own domain.

So I think it deserves some slack; maybe in a hundred years, when
it'll be dead obvious to everyone that ASL is a language and learning
language early — any language — is good for kids, and for that matter
it's a damn useful language to know even for hearing people to use
with each other, and it's rather pretty and linguistically
interesting, and Deaf culture isn't under attack… maybe then they'll
be more open to us hearing folk meddling with their language. ;-)

That doesn't make the silly criticisms less so, but it gives some
context. Besides which, as David eloquently explained, SignWriting
*does* kinda suck vs what could be done. I take that just as an open
engelanging challenge, albeit not one that I choose to take up. (UNLWS
gets all my conlanging attention these days.)

I have made a couple signs on the fly when needed, though. :-P If you
respect the morphological and phonaesthetic conventions of the
language, it's fine to do so and IME deaf folk are OK with it. (There
again you have to remember the context of the linguistic atrocity that
is SEE/SEE2, which totally fails at this and is the standard most deaf
people have of "hearing people made signs". You have to show you're
not that dense if you want someone to accept a sign you made up — and
it has to be novel enough that there isn't already a standard one
that's probably better anyway.)

(In case you're wondering: one sign I made was for a meditation
technique I call 'invocation' in English; in ASL I modified one of the
signs for 'copy' onto the location used for various thinking related
terms. My Deaf conversant understood immediately, which was nice.)

- Sai