That is either Guldentrader, Litebit or Nocks btc address buying Gulden for users who purchase from those sites.
I notice Nocks almost has the same amount of buy support as Bittrex, Nocks will become the biggest exchange for Gulden by end of the month. This is very good for Gulden.
There is a lot more Euro then btc to buy Gulden with and soon people will be able to earn interest with Gulden.
Nocks is leading the charge today, bittrex traders will be waiting to see if bitcoin will rally that the New Year holiday period is over. On some days I have seen bittrex ahead on price but today it's behind Nocks by some margin.
Bittrex traders will come in fast once the Gulden developers finally give an official release date for PoW2 and SegSig.