I think it is just what the IATA uses since Baltia is a member with them now. Kinda like the FAA has Baltia as BLT. The link below is to look up airlines on IATA's website with the two letter designation give to each airline by the IATA. Baltia does not come up yet on the website.

http://www.iata.org/about/members/Pages/airline-list.aspx