I just wrote a piece about plinking.
Almost every person I've talked to about their experiences in the Old Sanctuary tells me about plinking.
Many Reform congregations sold seats for the High Holidays during the 19th century to make money. Some auctioned them off. Lots of Protestant congregations did too. The practice fell out of fashion in the 20th century. Though I still remember my parents having assigned seats during the High Holiday services in the 1950s and 1960s. The whole ushering thing. Where the men congregation leaders would take the family tickets, the wife would take their arm, the husband and children trailing behind and show them to their seats.
Anyway, when they built the Old Sanctuary, Nathan Eckstein oversaw the selling of the seats. The treasury was just about empty (or worse) by the time the building was done. And the selling of the seats refilled the treasury.
Initially there were metal card holders on top of the seats displaying the 'owners' of those seats. Eventually they discontinued that practice.
But the metal card holders remained on the back of the seats.
The children of the congregation soon realized that, if you snapped the card holder with your finger, it made a very satisfying plinking noise.
Plink, plink, plink. For years, the kids plinked the card holders before and after services. The more adventurous plinked during the service. Sometimes they got in trouble, sometimes not. But they loved that little noise. The younger children watched the older kids plink those holders. They wanted to do it too. And they did.
I don't know what the card holders looked like. Maybe I will ask somebody to draw one.