o/~ Come and meet the Letter People, Come and visit the family! Words are made of Letter People, A-B-C-D, follow me! o/~
Show that was broadcast on KETC (Channel 9 - St. Louis PBS) during the early/mid 80's detailing the adventures of the Letter People, a race of beings living in Letter People Land.
Basically, to be a proper Letter Person, you had to have a sound. In rare cases, it had to be given to you, like in the case of Mr. X (Messirs K and S graciously allowed him to use their sound, because he was causing random chaotic effects in Letter People Land) Mostly, you already had it / discovered it.
The Letter People
Servo5678 adds "The Letter People also existed as inflatable "huggables" for use in kindergartens. I remember these guys from my own elementary school days in 1986."
Thanks also to Servo5678 for letting me know about Mr. Y's claim to fame.