While cleaning out the washing Machine, Luis pulled out Teeny little Superguy, cup and all. And they even played a bar of the theme song with it. Looks like these gems are going to be a lot more obvious from now on. At least, more obvious than something out of focus you can kind of see in widescreen under the PBS logo.
There were a couple other musical prompts (Oscar's I Love Trash played when he picked up his lint ball, some sort of tune that seemed familiar when Elmo was looking for the wrench), but I don't know if they count.