"56k modem" found in VHF band
160MHz lies in the Marine VHF Radio Band.

I guess the signal you received is for the marine vessel tracking system called  AIS (Automatic identification system). In section Technical Specification of the Wikipedia Article you find that it 
uses 2 channels at 161.975MHz and 162.025MHz and carries a 1200baud digital signal which fits to the details you mentioned.

EDIT:
The signal you received is probably a DSC (Digital Selective Calling) transmission used in Marine VHF Communication (It is used to selectively call one particular maritime radio station).

See ITU-R M.493-12 Specifcation:


  1.3.2 Frequency modulation with a pre-emphasis of 6 dB/octave (phase
  modulation) with frequency-shift of the modulating sub-carrier for use
  on VHF channels:
  
  
  frequency-shift between 1 300 and 2 100 Hz; the sub-carrier being at 1 700 Hz  
  the frequency tolerance of the 1 300 and 2 100 Hz tones is ± 10 Hz; the modulation rate is 1 200 Bd;
  the index of modulation is 2.0 ± 10%.