The most interesting ideas I found were at
http://mappingcenter.esri.com/index.cfm?fa=ask.answers&q=878
That's not so easy as a fill symbol--you could convert the fill
symbols of your landslide layer to representations and then
individually rotate the arrow markers within those fill symbols (that
might get really tedious).
If you've got an elevation dataset you could do the following:
Use the Aspect tool in either the Spatial or 3D Analyst extensions. That will produce an output raster with values that
represent downhill azimuths. (This assumes that gravity is in play in
the sense that flow movement is being derived from an after the fact
elevation dataset where downhill movement is assumed to be the path of
least resistance.)
The idea here is to produce a point dataset from the Aspect raster. But, depending on your map scale you will likely need to
reduce the resolution of the Aspect raster before using the Raster to
Point tool. To do that use the Aggregate tool in the Spatial Anaylst.
Once you have an acceptable outcome from the Raster to Point tool for your map scale (density of points is not too dense or too sparse),
then I would add a Short Integer field to the point dataset to have a
value of 0 for outside the landslide areas, or 1 for inside the
landslide areas. First calculate all values to 0, and then use Select
by Location to select the points inside your landslide areas and
calculate that field's value to 1. That will allow you optionally
include (via definition query) or symbolize differently the points
outside the landslide areas.
This will result in a more regularly spaced look, like the bottommost
of your scans.
Another option, particularly, if you want a more hand rendered look
(like the uppermost of your attached scans), you could hand-digitize
flow lines and then use cartographic representations on those. We
explain how to set up that kind of symbology on the Mapping Center
blog when talking about symbolizing one-way streets. You could
control the spacing and offsets of each flowline's symbol, creating a
similarly expressive effect as shown in your attachments.