It's not fair to say we've ever seen the 50 day MA cross the 200 day MA to the upside on decent volume.
The first time around (early 2012) was so early on, however lead to a 2 year rally.
The second time around (July 2014) was on very low volume and couldn't break above recent highs so broke down.
This time around, we have decent volume, already above recent highs and lots of positive (for BTC) market forces at play. This is typically a strong indicator of the beginning of a strong upward trend.
The first time around (early 2012) was so early on, however lead to a 2 year rally.
The second time around (July 2014) was on very low volume and couldn't break above recent highs so broke down.
This time around, we have decent volume, already above recent highs and lots of positive (for BTC) market forces at play. This is typically a strong indicator of the beginning of a strong upward trend.