How much can you "see" of the contracts being signed? Is it a "we just promise not to look, much" or are they encrypted such that you need customer permission to view?
We would not need a customer's key in order to access a contract. However, only certain members of our team have the ability to access contracts, and they only do that when needed for support or to fix a bug. We log all instances of accessing a customer's account.
Stats like those I shared above are from a combination of what users tell us and from aggregated, anonymized metrics across our app.