What green Filter icon means?

Filter Icon
If your worksheet contains hidden rows xlCompare notifies you that some of the data is hidden.
Database tab on the ribbon contains set of commands to manipulate visible and hidden data.
Include Hidden Rows option on the Filter tab includes or excludes hidden data from comparison. So, this icon is important. It says that there is a data which may be missed.
To show all rows on this sheet, use Cancel Filter command on the Database tab.