Draw icon next to object that have a specific component. Must be matching a [editor data]/icons/icon_[Type].png as first child (after Transform).

EditorTypeIconDrawer.cs

using UnityEngine;
using UnityEditor;
using System;
using System.Collections.Generic;

[InitializeOnLoad]
public class EditorTypeIconDrawer
{
  private static Dictionary<Type,Texture> icons;

  private static bool isRegistered = false;
  
  static EditorTypeIconDrawer()
  {
    RegisterGUI(true);

    if (icons == null) icons = new Dictionary<Type, Texture>();

    foreach(KeyValuePair<Type, Texture> icon in icons)
    {
      Debug.Log(icon.Key);
    }
  }
  
  static private void RegisterGUI(bool register)
  {
    if (register)
    {
      if (!isRegistered)
      {
        EditorApplication.hierarchyWindowItemOnGUI += HierarchyWindowItemOnGUI;
        EditorApplication.update += Update;
        isRegistered = true;
      }
    }
    else
    {
      EditorApplication.hierarchyWindowItemOnGUI -= HierarchyWindowItemOnGUI;
      EditorApplication.update -= Update;
      isRegistered = false;
    }

  }
  
  static void Update()
  {
    //foreach (KeyValuePair<Type, Texture> icon in icons) if(icon.Value != null) Debug.Log(icon.Key + " ? " + icon.Value);

    EditorApplication.RepaintHierarchyWindow();
  }
  
  static private Texture refreshIcon(Type componentType)
  {
    if (icons.ContainsKey(componentType) && icons[componentType] != null) return icons[componentType];
    
    Texture icon = (Texture)EditorGUIUtility.Load("icons/icon_" + componentType.ToString() + ".png");
    
    if (icons.ContainsKey(componentType)) icons[componentType] = icon;
    else icons.Add(componentType, icon);

    return icon;
  }


  static private void HierarchyWindowItemOnGUI(int selectionID, Rect selectionRect)
  {
    GameObject go = (GameObject)EditorUtility.InstanceIDToObject(selectionID);

    if (go == null) return;

    Component[] comps = go.GetComponents<Component>();

    if (comps.Length < 2) return;

    Component firstComp = go.GetComponents<Component>()[1];

    //Debug.Log(firstComp.GetType());

    if (firstComp == null) return;
    
    //generate icon
    Texture icon = refreshIcon(firstComp.GetType());
    
    //no icon for that type
    if (icon == null) return;
    
    selectionRect.xMin -= (go.transform.childCount == 0) ? 15f : 29f;

    selectionRect.yMin += 1f;

    selectionRect.width = 14f;

    selectionRect.height = 14f;

    GUI.DrawTexture(selectionRect, icon);
    
  }


}