Character Shill

From the early days of TV and radio, this is a type of commercial where the action stops and the show's characters just talk about the sponsor. Sister trope to Enforced Plug, where the characters try to work the shill into the story itself.

Not to Be Confused With Creator's Pet. Or even The Shill, really. Or Character Shilling.

And Now A Word From Our Examples:

A documentary on Superman shows a commercial spot from The Adventures of Superman, with Clark and Jimmy enjoying a very sugary breakfast cereal together.
The Flintstones and I Love Lucy both had in-character ads for cigarettes.
Parodied on The Simpsons, with John F Kennedy and Richard Nixon pausing in the midst of their debate to plug Duff Beer.

Nixon: Well I would suggest, Mr. Vancouver, that if you knew the President that, that was just a facetious remark.
Announcer: And now a word from our sponsor.
Kennedy: I would like to take this opportunity to announce my fondness for, ah, Duff Beer. (audience cheers)
Nixon: I'd also like to express, er, my fondness for that particular beer. (audience grumbles)

The George Burns and Gracie Allen television show would feature segments with Harry Vonzelle(?) wandering around supermarkets and discussing Carnation Evaporated Milk.
30 Rock tends to turn Product Placement into this for the sake of humor.
The original Dragnet radio show featured breaks with Jack Webb (the actor for Joe Friday) advertising for Fatima Cigarettes.
Mercilessly mocked in Return of the Killer Tomatoes!, where the director claimed to run out of money halfway through the movie, prompting the cast to blatantly plug various products and companies until one guy gets sick of it and asks "Do we have enough money to finish this turkey yet?"
Parodied in Italian Spiderman when our hero (who's already chainsmoking his way through the entire film anyway) takes time out to do nothing except really enjoy a fictional Il Gallo brand cigarette and reflect on how good it is for a while.