I believe it is pretty much standard that the Mark is the lower RF
frequency. For AFSK using a SSB transmitter that means that the audio
Mark tone is the higher frequency and the transmitter is set to LSB
which inverts it to the lower RF frequency.

For amateur and most commercial operation, the RF Mark frequency is
generally given as the assigned frequency. The military uses the
center, half way between Mark and Space as the assigned frequency.
Because they assign channel frequencies as the center of the assigned
bandwidth, this always puts the FSK signal in the center of the
channel.