Inside wviz, the "package://" syntax does not work as you might think. Since web interfaces typically do not have access to your entire file system, they cannot load meshes from arbitrary packages. Thus, wviz will replace "package://" with "resources/". That is, it will look for meshes within the "resources" directory in your base web directory. Note that only Collada models will load. I am not sure if triangle lists are supported (my guess is yes, but I am not sure).
Also note that wviz in its current form is currently deprecated. New efforts are being made with Robot Web Tools (http://robotwebtools.org
). In particular, you will want to look at ros3djs (https://github.com/RobotWebTools/ros3djs
). An example of markers can be found in https://github.com/RobotWebTools/ros3djs/blob/stable/examples/markers.html