All routes out of the Horseshoe Meadows area are clearly marked other then Army pass, I cannot recall any sign indicating
Army Pass at all since it is no longer maintained but all routes to
New Army are
marked , what isn't marked is when you reach the top of either, you will have to know to begin down hill west where there is a trail.
Now of course your not going to have a
sign at any of these locations that says Mt Whitney this way but a brief scan of the map can leave you without doubt of where to go.