From the 2005 NEC.
"820.50 Listing, Marking, and Installation of Coaxial Cables.
Coaxial cables in a building shall be listed as being suitable for the purpose, and cables shall be marked in accordance with Table 820.50. The cable voltage rating shall not be marked on the cable.
FPN: Voltage markings on cables could be misinterpreted to suggest that the cables may be suitable for Class 1, electric light, and power applications.
Exception No. 1: Voltage markings shall be permitted where the cable has multiple listings and voltage marking is required for one or more of the listings.
Exception No. 2: Listing and marking shall not be required where the cable enters the building from the outside and is run in rigid metal conduit or intermediate metal conduit, and such conduits are grounded to an electrode in accordance with 820.40(B).
Exception No. 3: Listing and marking shall not be required where the length of the cable within the building, measured from its point of entrance, does not exceed 15 m (50 ft) and the cable enters the building from the outside and is terminated at a grounding block."
Don