What does this Icon Question Mark mean?

roncruiser That is a Numeric range parameter. You can create one from the Home tab in Power BI and going to Modeling, then New parameter and then Numeric range.

Hi roncruiser ,

This happens when we create field parameter in power bi desktop. 

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Hi roncruiser 

That question mark is an extended property auto-added to a column when creating a numeric or field parameter using the GUI. As a numeric parameter, the column can be added to a slicer as single select. The same property can be applied to  any numeric column using Tabular Editor which is useful if the column is, say, in a fact table and not a what-if parameter table. Otherwise, you can just create a new numeric parameter from the modeling tab