That is correct. The DTMF tones were used on numerous cable networks in the 1980s to trigger local spots. MTV was the first network I specifically recall using this system, though the main CNN network also used it at the time. CNN Headline News was carried by many OTA stations as time filler, as its 30 minute program wheel fit into their schedules.
Those 1980s DTMF cue tones were never actually meant to be audible to the public, ever. They were only heard on some cable channels, on some cable systems, due to human error.
Cable network feeds on C-band satellite transponders back then employed analog
subcarriers for sound. The frequencies for the subcarriers, and the total number of them, was arbitrary from one transponder to the next. 6.2 MHz for left, 6.8 MHz for right, and 5.8 MHz for mono was common, but not always the case. Cable TV networks that offered local ad insertion avails to cable systems would typically transmit a duplicate copy of their normal audio, one containing their DTMF cue tones, on a dedicated audio subcarrier frequency meant only to drive cable company VTR banks. For example, Nickelodeon might have 5.8 MHz mono plus 5.2 MHz mono with cue tones. And MTV might have 6.2 left, 6.8 right, 5.2 mono, and 5.8 mono with tones. Well, cable head end technicians would always receive technical literature telling them which subcarriers to modulate onto the coax for their subscribers, and which to route to their VTR banks for cue detection. But they didn't always read those faxes carefully. If your cable company head end tech setup the MTV IRD by blindly dialing in 5.8 for mono out of habit, but didn't notice his fax sheet from MTV indicating "public" mono on 5.2 MHz (with 5.8 MHz actually being its cue-toned mono), then everyone in your city would constantly be pestered by those tones. But only on MTV, and not on any of the other channels he tuned his head end's IRDs correctly for. Meanwhile, the next city over's cable system might have their IRD tuned for MTV correctly, sparing viewers from hearing anything amiss. But then
they might have screwed up A&E...
The phenomenon of hearing DTMF cue tones slowly began to desist in the second half of the '80s, when the cable networks began adopting VideoCipher II scrambling for their C-band feeds. VCII carried the audio digitally and only supported two channels (left and right). At that point, cues became separate connectors on the backs of satellite IRDs that lazy or clumsy technicians could not easily mistake for subscriber audio outputs.
You can see an example of the VCII's digital audio in
this screen capture. VCII basically turned the horizontal blanking interval into one very tall QR code.
