Hello,
New to Unity, been playing with it for a few weeks and have searched for a way to show the GameObject in the scene view whether selected or not. I’d like at least an icon, a cross or gizmo to be visible at all times. Is this possible? Is there a script or plugin I can use? I can’t understand why these aren’t visible by default because they are so core to everything else.
Thanks for your time.
I would guess the assumption is that most game objects will have some sort of visual associated with them, so displaying an additional icon by default for all game objects would just clutter up the scene view. (People already ask how to turn off gizmos such as those for audio sources and so on, so I doubt people would really want a whole other group of gizmos to be displayed by default.)
Fortunately, for cases where you have game objects that don’t have a visual associated with them and that you’d like to be able to see and manipulate easily (e.g. waypoints for a pathfinding system), Unity’s got you covered: check out OnDrawGizmos() and OnDrawGizmosSelected().
Null objects (and colliders) should have a default icon since they can’t visibly be selected, whereas everything else is selectable since you can see it. An icon would be visible for empty objects and the icon would be overridden when outfitted with a component. Also, colliders, mesh renderers, and other components would have visible icons as well.
You should also be able to turn off all the icons or only certain ones in the scene view.
Well, you can always submit a feature request 
I made a feature request here: http://feedback.unity3d.com/forums/15792-unity/suggestions/1237649-a-scene-view-visual-icon-or-other-representation-f?ref=title
If anyone wants this to happen, please vote for it.
Or you can also code few tool to handle that , which I did for quickly hide show all or selected “collider / trigger” in my scene for example.
Using editor class you can pretty much make what you need for various situation.