For the record, there are a number of different station types that do not require any form of identification whatsoever, including wireless telemetry (i.e. SCADA systems used by utilities, farmers etc.) Radar stations need not identify, in spite of transmitting RF. Automatic vehicle locators, ala Lojack, are also exempt. Paging stations also need not identify themselves, and in a curious twist of FCC rulemaking, there’s actually a great deal of voice (phone) communications occurring under paging authorizations.
Then we have Part 15 transmitters, which could not possibly transmit a call sign because none exist, in spite of their “licensed by rule” status.
To be clear: All radio in the transmissions in the US require a “license” in the most literal sense. However, many of those “licenses” are granted by “rule” instead of “application.”
There is a huge niche in legal practice dedicated to telecommunications law.
The FCC does care how a station labels itself outside of call letters.
The old KISN-AM in Portland was officially sited in Vancouver, WA across the river. But it didn’t want to be known as a Vancouver station and used labels and slogans to imply it was a Portland station. (Its main studio was in Portland as well as its transmitters. But it’s “official” address was a dumpy office in Vancouver.) So the FCC would occasionally order them to cut it out. (The station owner caused so much trouble over the years it became one of the few stations to lose its license.)
One trick was to say “KISN 910” pause “Portland weather is …”
(The station had been KVAN, country-western, and switched to KISN, rock and roll, causing one of its DJs to quit and head home. I wonder what Willie Nelson’s career would have been if he stayed on.)
There are also sometimes fights over radio stations using “rounded” frequency ids. E.g., stations at 99.7 and 100.5 both using “100” in their label. I don’t think the FCC gets involved is those disputes.
Before the proliferation of digital tuners, it may have been sufficient to identify a station as “K99” if its frequency were, say 98.7 or 99.1, as many in this area did. Today, you better be specific. We have stations on pretty much every frequency in the commercial band here (92.1-107.9 Mhz)
Here in Peru, although there is a technical call ltter combination for stations, they are unknown for besically everyone. TV channels and radio stations were always names, since many were country-wide.