Here is the blessing for the washing of the hands translated into sign language. Since a person's hands are active and might have come in contact with something unclean or impure, one must wash his/her hands before consuming the challah.

https://youtu.be/NYP9EGeorRc?list=PLsbhjqXRyC9q2SvhDHAGxd1yUUQr938iG


Type of Custom: Kiddush, Motzi & Handwashing

Holiday/Event: Shabbat

Source: Custom & Craft