Answer: PSST

AnswerCrossword Clue
PSSTHushed "Hey!"
PSSTSound from a note passer
PSST"Hey you!"
PSST"You there!"
PSST"Hey there!"
PSST"Yo!" quietly
PSSTCall for attention
PSSTHissed "Hey!"
PSSTSibilant "Hey, you!"
PSST"Hey!," in a library
PSSTHissed "Hey you!"
PSST"Hey, listen up!"
PSSTMuffled "Yo!"
PSSTSibilant attention-getter
PSSTSubtle alert
PSSTHushed "Hey you!"
PSSTSibilant "Over here!"
PSST"Hey!" in class
PSSTHey, the quiet way
PSSTNote passer's signal
psst(used to attract someone's attention in an unobtrusive manner)
PSSTFurtive "Hey!"
PSSTAttention-getter
PSST"Hey you, c'mere!"
PSST"Hey, over here!"
PSSTAttention getter
PSSTSibilant attention getter
PSSTSubtle "Over here!"
PSSTVerbal nudge
PSSTSibilant summons
PSSTAttention-getting sound
PSST"Hey, you!"
PSSTSibilant "hey"
PSSTConspiratorial "Hey!"
PSSTFurtive whisper
PSSTHead-turner
PSSTSibilant "Hey!"
PSST"Over here!"
PSSTSibilant "Ahem!"
PSSTHey, over here!