To put on the long finger

while most people agree on the meaning of this phrase, I am curious to know if anyone can fill me in on the origin of it....

I've never heard the expression (I live in the U.S.). What does it mean and how is it used?

It means "to postpone something indefinitely." It is in common usage here in Ireland and, according to one website, is an Irish colloquialism, which I hadn't realised. "Méar fada" is Irish for "middle finger." The Dictionary of Hiberno-English has: "on the méar fhada," postponed indefinitely. 'Fraid I have absolutely no idea why it has this meaning.

I've never heard it in the UK. I guess it hasn't travelled far, and may even be regional within Ireland.

Jonathon Green labels it "Irish."

put on the long finger, to phr [20C] (Irish) to postpone indefinitely. [one pushes it as far away as one can]
From Cassell's Dictionary of Slang

I couldn't find anything in my references. I am wondering if it could have anything to do with tying a string on your finger to remember something?