Nudity is prohibited on over-the-air broadcast television between 4AM and 10PM local time. (Since national networks broadcast primetime from 7PM-10PM in the Central Time Zone, and they use the same feed, at the same time, for the Eastern Time Zone, that means that nudity is not ostensibly precluded from the 10PM-11PM timeslot even in the Eastern Time Zone.)
Other than that (i.e., for over-the-air broadcast television stations, between 10PM and 4AM local time, and for all cable networks), the broadcasters (obviously with a lot of input from sponsors) determine what kind of programming they present, and to what standards, as a reflection of the First Amendment rights guaranteed by our Constitution.
TCM is not an over-the-air broadcaster, so they're not subject to any specific governmental limits.
Viewers who prefer not to see certain programming should purchase television equipment with a V-chip, and use it. If certain networks fail to provide adequate warning of what type of programming they're presenting, viewers should complain to the network, and avoid tuning in that channel.