NEC 725.179(J) covers the listing and marking of Class 2, Class 3, and Power Limited Tray Cable (PLTC) cables and describes their intended use:

• A cable marked CL2 indicates that the cable is for Class 2 applications.
• A cable marked CL3 indicates that the cable is for Class 3 applications.
• A cable marked with an “R” as the last letter indicates that the cable is suitable for use in riser applications (vertical runs penetrating one or more floors and in vertical runs in a shaft). An example is a CL2R cable. This is a Class 2 riser rated cable.
• A cable marked with a “P” as the last letter indicates that the cable has been evaluated for use in a plenum. An example is a CL2P cable. This is a Class 2 plenum rated cable.

Below is a sample of NFPA 731. For the complete section, see the actual NFPA 731 text at NFPA.ORG. Once there, click on the free access link to the latest edition of NFPA 731.

4.6.3 Wiring. 

4.6.3.1 The installation of all wiring, cable, and equipment shall be performed in accordance with NFPA 70, Article 725 or Article 800, where applicable.

Below is a sample of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the latest NEC^® edition of NFPA 70.

725.179 Listing and Marking of Class 2, Class 3, and Type PLTC Cables.

(A) Types CL2P and CL3P. Types CL2P and CL3P plenum cable shall be listed as suitable for use in ducts, plenums, and other space for environmental air and shall be listed as having adequate fire-resistant and low-smoke producing characteristics.

(B) Types CL2R and CL3R. Types CL2R and CL3R riser cables shall be marked as Type CL2R or CL3R, respectively, and be listed as suitable for use in a vertical run in a shaft or from floor to floor and shall be listed as having fire-resistant characteristics capable of preventing the carrying of fire from floor to floor.

(D) Types CL2X and CL3X. Types CL2X and CL3X limited-use cables shall be marked as Type CL2X or CL3X, and be listed as suitable for use in dwellings and raceways and shall be listed as resistant to flame spread.