How do you spell the sound shssss for quiet please?

Oh, dude, you're asking me to spell out a sound? Like, really? Okay, here it goes - "shssss." Yep, that's it. Just a bunch of random letters that kinda mimic the sound you're trying to spell out. But seriously, who spells out sounds? That's like trying to write down a drum solo - it just doesn't work.