Haha. I was a banker for years, and this came up many times. At my bank, we had meeting about this very thing (very productive use of our time, huh?) We went thorough a phase where we stocked up on pens with our bank logo hoping people would take them. And people DID take them. We couldn't order them fast enough. Then, we resorted to putting out pens with no caps, because........ who wants a pen with no cap? That actually worked really well.
It's not that the bank is too cheap to give you a pen. It's more because no one was hired to monitor each and every station where people used the pens to make sure one was there. If one customer took a pen, we didn't have time to run out there after each customer left and make sure a pen was available for the next customer. And how mad would you be if there was NO pen at your bank, chained or otherwise? At the teller stations, we didn't have time to keep running back to the stock room to grab more pens. As far as trusting customers....well, they DID steal the pens.
I saw a big sign in the window at a TD bank in NYC that read: "What other bank would let you take our pens home?" It kind of pissed me off. I thought, You make millions off of people, and all they get is this cheap, lousy, pen which is free advertising for you? UGH. Anyway, there object is to say "Come on in you can trust us, but we can't trust you" lol