Last night I did a presentation (on poetry) at the local library. It was packed with a lot of information, only some of which was covered in the handout. It was requested that I pass the slides to the library for them to send out to the participants. I don't mind doing that, but feel like I should put a copyright notice or something on it. I don't know that it is necessary and might be overkill, as my name is on the first slide. Should I further mark the slides to establish ownership?
Consider the context. Libraries are for the public good and they provide knowledge to everyone for free. It's probably the goal of every librarian to have the most complete information, available to the majority people, in the most accessible formats.
Naturally, you and the library have no control over who will read the information in the future, and what nefarious purposes they will use it for. What is the "worst-case scenario", that someone will put a single slide up on the internet without your name attached? It can't be that a student will use the research to pursue their own path to knowledge because otherwise why did you hold the talk in a library?
If a particular slide quotes your personal ideas that are perhaps at the core of your PhD dissertation that will be published independently of the talk, sure, put your name on that slide and declare your authorship.
But if the slide is another poet's words, or someone else's history, or the result of your own journey to knowledge which has probably involved free information from an unremembered author you read at a library, are you really losing anything personal or tangible?
What is the "best case scenario", that you inspire someone to learn about poetry?
The library will (obsessively) attempt to keep all the materials of the talk together and indexed for their archives. They will include your title slides and more importantly the metadata that will show up in catalog searches. When you give them the slides, add a cover letter or attachment with all the relevant metadata information to identify you as the event speaker (including a brief bio that indicates your authority on the topic), whether or not you add your name and URL to each and every slide.