There is a slight distortion of the background that shows the location of an invisible character. Found in the Prison Barracks. Gonch has it. Edith gives you this ring once you have saved her son. The higher the level, the better the golem.
Higher scrolls replace weaker ones.
The first one is found in Glass Palace. Use the Ice Key in the foyer to find it. The second is found after your bout with the plague king. The third one is found in the Library of Gno when you have the Gold Key. Found in the chest in the Airlock.