I am reliably informed that yesterday (14th March) is written as ‘3/14’ by inhabitants of lands across the western ocean.* It follows that for the transcendentally-minded citizens of these lands, yesterday was ∏-day.
*I’m not so sure about the punctuation but the ordering of “month, then day” is the important point here.
My informant also told me that ∏-day is celebrated by the ritual eating of pie at 1:59 on this day. My informant wasn’t able to tell me what sort of pie is eaten. There’s more about this day here. In particular, it is not to be confused with National Pie Day, which is 23rd January.