From German - English Ding/FreeDict dictionary ver. 1.9-fd1:
Sch! /ˌɛstsˌeːhˈɑː/ <int>
Hush! Shush! <int>, Ssh! <int>, Shh! <int>, Whist! <int> [Sc.] [Ir.] , Whisht! <int> [Sc.] [Ir.] , Wheesht! <int> [Sc.] [Ir.] , Hist! <int> [archaic]
Note: used to call for silence
Synonyms: Pst!, Psst!, Pscht!
see: pst! sagen
Note: Aufforderung zum Stillsein