There should be a highly salient visual flag on the interface whenever filters have been applied to a found set. As it is, the only cue is a subtle shift in the appearance of the column header, which may not even be visible onscreen at any given time. DV might take a cue from Auto Trader's website, which has a notice at the upper left displaying how many filters have been applied: e.g., FILTERS 3.
This is especially important because DV retains filters, so if you run a new search, existing filters remain in effect. It's entirely too easy to run a search in DV without realizing that applicable records may be hidden by a filter which the user doesn't realize is still being applied.
And also add a "clear all filters" option to reset everything
They do have a Clear All button at upper left. It's odd that they didn't label it "Clear All Filters" though.