This dual suffix is also often represented by writing the phonetic or determinative glyph twice, e.g. tꜣwj:
References
Loprieno, Antonio (1995) Ancient Egyptian: A Linguistic Introduction, Cambridge: Cambridge University Press, →ISBN, page 60
James P[eter] Allen (2010) Middle Egyptian: An Introduction to the Language and Culture of Hieroglyphs, 2nd edition, Cambridge: Cambridge University Press, →ISBN.