To help keep track of escalation on verbal intervention that would come before actual ‘rate cheks’ and then USD/JPY selling out of the Bank of Japan, here’s a guide:
The clear signals to watch for imminent Bank of Japan FX yen interventionHere’s what to watch for to warn of imminent Bank of Japan (BOJ) yen interventionThe 4 things to watch prior to Bank of Japan FX yen intervention
I wrote those posts last year but they are still relevant.
Kanda’s yen phone 
This article was written by Eamonn Sheridan at www.forexlive.com.