For more detail on rossko57’s answer, there’s a DP for that: Design Pattern: Encoding and Accessing Values in Rules, Approach 2.
I’ve also some approaches that work only with Scripted Automation, not Rules DSL. You can put a default value into the Item metadata and have a system started Rule that reads that metadata and updates the Item with it’s value. My Ephemeris Time of Day implementation uses this approach to initialize some Items to define static start times.
The heating icon uses ON and OFF only. Not a range. There is no representation in the icon for “AUTO”.