This was sent both by Emma who says “It may be simple, but I just don’t get it! Thanks!” and by padraig who claims “I actually did get this, but it was more like a picture puzzle than a cartoon”.
And padraig tries to clue us on what he meant by a picture puzzle by adding “The pigeon is standing on a…..” But if he’s being a stool-pigeon, why is it what the cardinal will say that is being made an issue? I’m still thinking mostly they are contesting who will be the top dog, erm, bird.
(And by the way, as long as it’s still signed as Wayno & Piraro we think it should be tagged as both Wayno and Piraro. And their blogs often discuss their collaboration, and make it clear that altho Wayno scripts and draws the Mon-Sat cartoons, Piraro consults and gives a lot of input as well.)
Comics I Don't Understand 
I think the cardinal doesn’t want to reveal anything to a stool pigeon, worried he’ll blab and tell the authorities. Once he steps down from the store, he is simply a pigeon. I think that’s all there is to it.
Targuman has it
Agree with Targuman
I agree with all three of you.
I concur.
I saw the cartoon in the paper and I got it right away. But I wonder if you have to be a geezer to know what a stool pigeon is.
This reminds me of a time in first or second grade when the teacher had us write down as many words with “oo” that we could think of. I wrote a whole bunch, including “stoopid” and “stoopidjin.” I didn’t really know what a stoopidjin was but I had heard it on TV. I probably thought it was a stoopid person.
I don’t know about the geezer part, since I am one. But the American usage goes back about 200 years, and before that was used as far back as Shakespeare’s time in the original meaning as bait for a trap…i.e. like a pigeon tied to a stool which was wobbled to make it flap its wings and draw in the curious flock.