Seen at a gas station:
You know your UI has usability issues when people tape multiple signs on your gas pump to help people get through the intricate and error-prone process of purchasing fuel.
Why does the upper note exist? The trouble is that there’s a Debit button but not a Credit button, and so since Credit is the default, users need to remember to override the default before swiping the card. People will sometimes naturally forget the special step because there was originally no reminder that this needed to be done, and because most other pumps don’t work that way. One solution would be to print the information prominently near the card reader, thus standardizing the note and making it more visible. A better and simpler solution would be to do what most pumps do: Avoid the opportunity for forgetting to specify the right thing by having both buttons, Debit and Credit, and simply prompting the user to press one or the other after they swipe their card.
But the trouble behind the lower note is even more blatant and, frankly, inexcusable: Is there any good reason not to conditionally print “ENTER PIN” or “ENTER ZIP,” instead of just always printing “ENTER DATA” which is not only unclear but also one of the classic geeky words to avoid in a consumer-oriented UI?
Then again, I’m amazed that in this day and age I still see output like “1 item(s) purchased.” Apparently it’s still more important to write the programmer-friendly printf( “%d item(s)”, count ) than the user-friendly printf( “%d item%s”, count, (count==1 ? “” : “s”) ).