Some sort of indicator, perhaps clickable to bring up a list or similiar showing which columns have filters applied and there expression / condition.
Also saying if the column is hidden or visible.
Ex. of information:
Filtered columns:
------------------
Name: Col a
Condition: 'contain' value 'test'
Visibility: hidden
Possibility to clear / modify certain filters directly from this list.
This could also have builtin warning in regards to hide columns...saying that you are about to hide a column that has filter applied.
