Learning British Sign Language had been the idea of one of the muggleborm students in the DA fifth year. It was only used by muggles, as there was a magical solution to hearing loss, so none of the Death Eaters would know what it was, and it was dead handy in a situation when you had to say something without non-DA or Order members hearing. As it was, Abraxas just looked confused for a moment before he continued on to say what he had been about to when he stopped to observe the odd hand motions the unknown boy made to the girl who could not have been anything but his sister.