MIC

Key MIC in Live FH refers to an optional Market Identifier Code that further identifies the exchange where the security is traded.
This entry is used only when the Service entry is one of:
Stock Symbols

For example, XNCM for NASDAQ Capital Market.
A list of supported codes can be found at here
In particular, for the US the supported codes are: XNYS,XASE,BATS,ARCX,XNMS,XNCM,XNGS,IEXG