Here is an extract from the FAQ page we put together for the 2008 Cabin Fever "not a contest" ULR event.
What if I don't hear the stations call letters?
Call letters are not required to be heard for identification. What is required is a judgment call by the participant. There should be sufficient information suitable to make the identification more likely than not. Typically, slogans, local phone numbers in commercials, weather information and other clues are suitable for identification.
For example you are tuned to 780 kHz and hear a weather report for "lake effects snow", or a program on the radio regarding the White Sox, Cubs, Bears or Bulls. You have heard WBBM more likely than not and can list it as heard and identified.
Example: you are on 780 and hear Spanish, but you don't know what is being said. You know that Venezuela Radio Coro is on 780. Because there are any number of stations in the US and Caribbean that are Spanish language, you can not say that this station is more likely than not Radio Coro. No ID.
You are tuned to 780 kHz and there is a weather report of ocean breezes and temperatures in the 80s. The announcer has an "islands" dialect or accent. The news reports that Governor Pearey is visiting England. That would be clues sufficient to identify ZBV