Unless you have never been to a lending library before, it should be a given that if you're borrowing items, you need to show your library card at the circulation desk so those items can be put on your account. You might be surprised to know that the majority of patrons checking out items place their items on the desk and just stand there until I ask to see their library card. Sometimes, patrons have their cards in their hands and will not relinquish them for dear life until I promise them that I will return it to them in a moment.
Maybe I'm just a crazy perch librarian, but to me, going to a library circulation desk and not automatically presenting your library card is like going to a store and not giving money to the cashier. Imagine the following scenario--Cashier: "That will be $5.25. [The customer stands and does nothing.] Can I have the money, please?" Seems a little ridiculous, doesn't it?
So, continuing our discussion on library etiquette, one thing you should bear in mind in the library when you're planning to check some items out is to "get carded"--present your library card at the circulation desk. Your friendly, neighborhood perch librarian would really appreciate it and thank you kindly for remembering.
Ever politely yours from the perch.