Take a look at this link from MDN... Math.sign().... https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign
Negative zero IS a valid usage! and the kata description does not say don't return a negative zero!

Yeah, if and else statements should have curly brackets (you can remove it if the following code is a single line).

You put the return true and return false in the same if statement, meaning it would always return true and never return false. The improvement I suggested would leave the return false outside the if statement and into the main body, leading to there always being a return statement.

You put the curly bracket in the wrong place.

Remove the curly brace after return false and put it before instead.