I was thinking about this poem today. It was from my first grade reading book (I was in an advanced reading group, so it might've been a 2nd great book). I think the book itself was called "Signposts."

Here's what I remembered:

Signposts, signposts
What do they say?
School ahead, or children at play
Don't feed the animals, stop, for sale
___________, don't lean on the rail.
Signposts, signposts ______________
And each is important in its very own way.

Thanks for helping me fill in the gaps! I think you are largely correct, and I think you are right that the word is "slow," not "stop."