Answer: pssst

AnswerCrossword Clue
PSSST

"Hey, you!"

PSSST

Insistent but covert attention grabber

PSSST

Sibilant summons

PSSST
"Hey there!"
PSSST
"Hey, buddy!"
PSSST"Your attention, please"
PSSST"Hey you!"
PSSSTCovert call
PSSST"Hey, buddy, over here!"
PSSST"Heyyy, buddy"
PSSST"Over here..."
PSSST"Hey, over here!"