This is the Exchange Code for the primary trading market for the security. It is displayed as a 3 digit alphabetical mnemonic. e.g. for the London Stock Exchange, the Exchange Code is ‘LSE’.
Many securities can be listed on multiple stock exchanges. This field can help distinguish between them. For example - Vodafone has the same ticker symbol on both LSE and NSQ markets, but may be distinguished using the exchange code.
For the LSE markets we publish the exchange segment in this field. The following are examples of segment codes - LON (London Stock Exchange), LSS (London SEATS Market), SEA (AIM Market), OFEX (PLUS Markets)