The most important difference, I'd say, is that you can express anything in a sign language.
So you are able to discuss abstract concepts.
I could tell you what I did at a conference abroad last week, in sign language.
Well, that's significantly more difficult using pantomime. It might be possible, but it's surely more difficult.
Also in relation to structure. You see, you use your whole body when using pantomime.
Whereas in a sign language you make use of a limited space, in front of you and next to you.
And so signs are depicted here.
Well, iconicity, that's an important key word, of course.
Or well, perhaps not of course.
Anyway, sign languages simply are more iconic than spoken languages.
I believe that's a simple fact, and why? Because it's easier to use your hands to...
...recreate the shape of objects or actions, easier than it is using your voice.
Nonetheless, a significant portion of the sign language lexicon isn't iconic at all.
And a part of the sign language lexicon, perhaps a larger part than we might think, is iconic.
An example I always like to use, if I were to show you two pictures, two men...
...and one is short and fat, and the other is tall and thin, and I tell you one of them is Tim, and the other is Bob.
Who's who? You would have a strong tendency to reply that the short, fat man is Bob.
Because B-O-B, the sound of that, recreates the shape in a way.