When you get the channel 6 building you have different options of programming. works just like jobs except you pay an amount and receive more at the end. The van, weather and dish unlock more programs
So I guess the Channel 6 icon would appear in a freind's town if they are currently broadcasting, and perhaps using the weather-thingy causes the sun/cloud to appear?
What is this weather-thingy? I only see the van and the dish available to buy.
Think of Channel 6 as Cletus' farm. You broadcast different programs and they each have a different icon. I would guess the icon appears over the building when it is ready to be collected. The weather station is built along the quest line for Channel 6 and opens a new broadcast option.