The Ancient Egyptian Mouth hieroglyph is Gardiner sign listed no. D21 for the shape of the mouth, being open, (therefore also implying a use for speech). The word 'mouth' was pronounced *rāˀ.
The mouth hieroglyph is used in the Ancient Egyptian language hieroglyphs for the alphabetic consonant letter r.
The Egyptian hieroglyph alphabetic letters
The following two tables show the Egyptian uniliteral signs. (24 letters, but multiple use hieroglyphs)
References
Mouth (hieroglyph) Wikipedia(Text) CC BY-SA