Armature Visualizer is a powerful gizmo for displaying armature bones in Unity3D. Drag-and-drop, select your armature, and you're done.
With support for both Skinned Mesh Renderer and transform-only armatures, Armature Visualizer can handle a wide variety of armature types. Armatures created with Blender are also supported.
Just like any other built in gizmo, Armature Visualizer can be toggled on and off via the Gizmo Menu. With one-click setup, no knowledge of coding is needed.