def extract_mark_posting(posting, config):
    """
    Extract mark from posting, if any.

    Args:
        posting: posting.
        config: A configuration string in JSON format given in source file.
    Returns:
        string of mark or False.
    """
    for alias in config['aliases_after']:
        if hasattr(posting, 'meta') and posting.meta and alias in posting.meta:
            return posting.meta[alias]
    return False
