š = the phoneme sh = Gardener Sign N37(pool-lake-basin) 1
Another Gardiner unlisted form has Gardiner no. N37, with two angled lines at the center of the horizontal block, and is used for the letter š (Wikipedia)
"The first usage of the Red Crown was in iconography as the symbol for Lower Egypt with the Nile Delta. Later it came to be used in the Egyptian language – as an alphabetic uniliteral, vertical form for letter "n" as a phoneme or preposition. It became functional in running hieroglyphic texts, where either the horizontal or vertical form preposition satisfied space requirements. The Red Crown is also used as a determinative, most notably in the word for deshret. It is also used in other words or names of gods. One older use of the red crown hieroglyph is to make the word: 'in'!, (formerly an-(a-with dot)-(the "vertical feather" hieroglyph a, plus the red crown). Egyptian "in" is used at the beginning of a text and translates as: Behold!, or Lo!, and is an emphatic." 21 Schumann-Antelme, and Rossini, 1998. Illustrated Hieroglyphics Handbook, uniliteral: U22, p. 60-61.