The 30th anniversary according to Google but surely it’s always been Pi day? We good calendar users (i.e. not Americans) have ‘Pi Approximation Day’ on 22/7 but given 22/7 is accurate to 2 decimal places how is it any more approximate than 3.14 being called Pi day.
ANYWAY, the main thing is that when you look at Pi Day on Wikipedia you get this picture and caption which is pretty much pure perfection: