I'm just saying that if you're going to say that sign language travels at the speed of light then so does text, or hyroglyphics or whatever.

Writing down the text takes time, in exactly the same way as moving your hands to the correct position in sign language. But then the transfer of the information, once formulated, is at the speed of light.

So either they both travel at the speed if light or neither does, depending how you want to think about it. Either way the OP statement is false.

But it also takes time to move your hands to use sign language, so then it doesn't travel at the speed of light either

Also, you know, reading