To “filter” those that hasn’t been processed by the previous run, is to compare the date of the last scenario run, to the date of the searched (latest) signed documents.
To do this, take a look at my recent answer on another topic : Automation is repeating every 15 min when the rule is greater than date - #13 by samliew
Hint: Your “From date” field should contain the “Timestamp” of the last scenario run, and you can probably leave the “To date” field empty.