Octave rlocus: format ploles and zero
Edit the rlocus.m file, in \share\octave\packages\control-3.1.0\rlocus.m

Change lines 291 to 294 from:

set (hplt(kk--), "markersize", 2);
if (! isempty (rlzer))
  set (hplt(kk--), "markersize", 2);
endif


to:

set (hplt(kk--), "markersize", 10);
if (! isempty (rlzer))
  set (hplt(kk--), "markersize", 10);
endif


Result: