YourJS candidate function: sameSign()

sameSign.js

function sameSign() {
  for (
    var args = arguments, b = args[0], mustBeNeg = b === b ? (b < 0 || 1 / b < 0) : NaN, i = args.length;
    b = args[--i], i && mustBeNeg === (b === b ? (b < 0 || 1 / b < 0) : NaN);
  );
  return !i;
}

//\\
sameSign(4, 0); // -> true
//\\
sameSign(0, 3); // -> true
//\\
sameSign(-0, 3); // -> false
//\\
sameSign(4, -0); // -> false
//\\
sameSign(-0, -3); // -> true
//\\
sameSign(-4, -0); // -> true
//\\
sameSign(-4, -3, -0); // -> true
//\\
sameSign(-4, -3, 0); // -> false
//\\
sameSign(-4, 3, -0); // -> false
//\\
sameSign(4, -3, -0); // -> false
//\\
sameSign(4, 3, -0); // -> false
//\\
sameSign(4, 3, 0); // -> true
//\\
sameSign(NaN, 3, 0); // -> false
//\\
sameSign(4, NaN, 0); // -> false
//\\
sameSign(4, 3, NaN); // -> false
//\\
sameSign(NaN, NaN, NaN); // -> false

https://www.yourjs.com/console?gist=f3813f782ca82c36ee6883fe87f6fbc0&file=sameSign.js