From MusiCAD

Vibrato as used by string instruments, voice etc. is usually left to the discretion of the performer. However, if necessary it may be written above the stave as:

  • poco vibrato or poco vib. for 'a little bit' of vibrato
  • molto vibrato or molto vib. for 'much' vibrato
  • senza vibrato or senza vib. for no vibrato at all