Avaz does not support Sign Language directly, however you can use some symbols from the in-built library 

Avaz uses the Symbostix library of images for the picture mode. The Symbolstix library has a rich content of 40,000+ symbols, of which there are approximately 600 symbols to denote Sign Language and you can use any of these symbols as images in Avaz. 

E.g. here are some examples

                        Close                                 Friend                                     More                                     Stop                              Thank you               

Click here to see How to add image or change the image