The A stands for applause. Thunderous even.
4 seconds sound clip from Snagglepuss - Paws for Applause (S1E9).
You can hear this line at 00:02:25.001 in the Blu-ray version of the episode.
Quote context
[...]
- I am a lenient man, Dimwitty. I'll give you... two minutes to produce a lion.
- But, P.J., that would take a miracle, even for TV.
- What knock on yonder doorway breaks?
- 'Tis I, Hamlet A. Snagglepuss.
- The A stands for applause. Thunderous even.
- It's a lion! Hello, miracle!
- How would you like to be a star?
- Oh, Snagglepuss, we're ready to roll.
- What's the idea? What's the idea?
- There's no star on my dressing room door.
[...]