On Bittrex now (BLK) renamed?
Same on cryptsy
i ended up on this thread trying to find the answer to this as well.
Was the symbol offically changed from BC to BLK?
Yes, so in case you are using them most trade pair links/apis at the exchanges have been changed, in addition to the quoted ones BTC38 is the most notable one as almost all BLK volume is currently against FIAT (CNY), about 4 million BLK only today.
Chinese like BLK much more because of some symbolic meanings. And i would also say that BitCoin could be named BC as well if it wasn't already named BTC, so BLK is perfect.