How to determine if an enum has been defined as a bitmask flag?

How would someone detect if an enum has been defined as a bitmask flag, or a series of single case values?

Example:

public enum ElementalType
{
    Normal = 0,
    Fire = 1,
    Frost = 2,
    Energy = 3,
    Nature = 4,
    Sonic = 5,
    Arcane = 6,
    Shadow = 7,
    Holy = 8,
}

Would be detected as a normal single-case enum.

However:

    public enum CubeFaceVisibility
    {
        None = 0,
        /// <summary>
        /// NegativeZ
        /// </summary>
        North = 1,
        /// <summary>
        /// PostiveX
        /// </summary>
        East = 2,
        /// <summary>
        /// PostiveZ
        /// </summary>
        South = 4,
        /// <summary>
        /// NegativeX
        /// </summary>
        West = 8,
        /// <summary>
        /// PositiveY
        /// </summary>
        Top = 16,
        /// <summary>
        /// NegativeY
        /// </summary>
        Bottom = 32,
        NorthSouth = North | South,
        EastWest = East | West,
        TopBottom = Top | Bottom,
        NorthEastSouthWest = North | East | South | West,
        All = North | South | West | East | Top | Bottom
    }

Would be detected as a bitmask style enum.

Does anyone know how to write a function that can determine the culture of enums? I'm tagging this as reflection, but that may be irrelevant to the question.