def METHOD_NAME(res):
    """Input a physical resolution string or value, output a formatted string tag to be used in filenames.
    """
    check_flag, res_value = is_physical_resolution(res, return_value=True)
    if check_flag:
        sigfigs = 0
        fmt_str = '{:.%df}'%(sigfigs)
        res_str = fmt_str.format(np.round(res_value, decimals=sigfigs)).replace('.','p') + "pc"
        return res_str
    else:
        raise Exception('The input resolution string "'+str(res)+'" is not a physical resolution!')
        return None