Discussion Forum—A Way with Words, a fun radio show and podcast about language

My friend and I have hit a road bump in a discussion about debt, the Jews, and Greenwich.  

What is the name the barrels, or something like "nails" or "nales," that were posted in the market places in the early 1900s in England? The may have looked like stone slabs, or made out of brass, possibly. They were markers that indicated where payment was to have been made for products in the market.  

For the life of me, I can't remember what they are named. I wish the Google Voice database afforded to this radio show were made public. It could very hold the answer I need.