The sign(x) function accepts only one value as its parameter.

x

A calculation which resolves to a number.

A number representing the sign of A:

• If x is positive, returns 1.
• If x is negative, returns -1.
• If x is positive zero, returns 0.
• If x is negative zero, returns -0.
• Otherwise, returns NaN.

<sign()> = 
  sign( <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>         |
  <dimension>      |
  <percentage>     |
  <calc-constant>  |
  ( <calc-sum> )   

<calc-constant> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN        

For example, in background-position positive percentages resolve to a negative length, and vice versa, if the background image is larger than the background area. Thus sign(10%) might return 1 or -1, depending on how the percentage is resolved! (Or even 0, if it's resolved against a zero length.)

div {
  background-position: sign(10%);
}

Another use case is to control the position of the element. Either a positive or a negative value.

div {
  position: absolute;
  top: calc(100px * sign(var(--value)));
}

• abs()