Name for value which may only be -1, 0 or 1?
There is no standard name, but the value can be seen as value in the balanced ternary numeral system or as the sign (sgn) function. IMHO, the name Sign() is more appropriate when working with calculations or ordering, the 'balanced ternary' is more appropriate when working with logic. For my purposes, I created a Tri enum in the C# language and, besides others, a generic mapping function with this code: 

    // https://en.wikipedia.org/wiki/Sign_function
    public static Tri Sgn&lt;T&gt;( this T value ) where T : IComparable&lt;T&gt; {
        var t = value.CompareTo( default( T ) );
        return t &lt; 0 ? Tri.Negative : t &gt; 0 ? Tri.Positive : Tri.Zero;
    }


And, last but not least, there is the three-valued logic: https://en.wikipedia.org/wiki/three-valued_logic. Values of the 'Tri' type can be used to implement functions for three-valued logic.