You might need to validate memos :)

def memo_is_valid(steemd_instance, memo):

    try:
        p = Post(memo, steemd_instance=steemd_instance)
    except ValueError as e:
        if 'Invalid identifier' in e.args[0]:
            return False
        raise
    except steembase.exceptions.PostDoesNotExist:
        return False

    return True