15 U.S.C. § 78o–8

(a) Rulemaking The Commission shall require, by rule, each nationally recognized statistical rating organization to establish, maintain, and enforce written policies and procedures that— (1) assess the probability that an issuer of a security or money market instrument will default, fail to make timely payments, or otherwise not make payments to investors in accordance with the terms of the security or money market instrument; (2) clearly define and disclose the meaning of any symbol used by the nationally recognized statistical rating organization to denote a credit rating; and (3) apply any symbol described in paragraph (2) in a manner that is consistent for all types of securities and money market instruments for which the symbol is used. (b) Rule of construction Nothing in this section shall prohibit a nationally recognized statistical rating organization from using distinct sets of symbols to denote credit ratings for different types of securities or money market instruments.