Since no radio stations in Europe uses call letters, if they did, what would their call letters will be like?
Based on ITU.
United Kingdom, maybe they be using G,M, V, or ZB-ZJ, ZN-ZO, ZQ. GBBC1 - For BBC Radio 1
As of 1934, both BBC London medium-wave transmitters (National Programme and Regional Programme) had the call sign G2LO, according to the Broadcasting Yearbook. Obviously, this was derived from the original 2LO.
Cadena Ser had the callsigns EAJ-1 in Barcelona and EAJ-7 in Madrid, when they broadcast on medium wave.
The original call sign for NRK in Oslo was LKO.
Some European countries had call letters for medium-wave and longwave transmitters at one time. It's hard to say whether any of them have survived internally as FM transmitter call signs, but with the amount of transmitter outsourcing nowadays in Europe, that's unlikely.