I think a slot for a credit/debit card isn't terribly intuitive, especially if the reader only accepts one orientation of the magnetic stripe, in which case a diagram is almost necessary.<p>There are readers that have asymmetric widths on the entry mechanism (strangely worded, but looks like [1]). This is an extremely subtle hint regarding the orientation (magnetic stripe goes with the wider part), that I would imagine the majority of people don't pick up on.<p>You might also look at this article [2] to see that legitimate ATMs do offer diagrams indicating the proper orientation of a magnetic stripe card.<p>[1] <a href="http://consumerist.com/images/31/2009/04/041909-008-shell-legit-card-slot-2.png" rel="nofollow">http://consumerist.com/images/31/2009/04/041909-008-shell-le...</a>
[2] <a href="http://consumerist.com/2009/04/heres-what-a-card-skimmer-looks-like-on-an-atm.html" rel="nofollow">http://consumerist.com/2009/04/heres-what-a-card-skimmer-loo...</a>