from typing import Any


def is_unknown(value: Any) -> bool:
    """ Returns True if the value is a common unknown indicator:
        ''        is True
        ' '       is True
        'na'      is True
        'NA'      is True
        'n/a'     is True
        'N/A'     is True
        'unk'     is True
        'unknown' is True
        '3'       is False
        '-3'      is False
        '33.22'   is False
        '4,333'   is False
        '$3'      is False
        'b'       is False
        3         is False
        3.3       is False
        None      is False
    """
    unk_vals = ['na', 'n/a', 'unk', 'unknown', '']
    try:
        return value.strip().lower() in unk_vals
    except AttributeError:
        return False
    except TypeError:
        return False