how to present a talk on work in preparation
If the work corresponds to a paper submitted to a conference, I put in the slides "submitted to conference X". Otherwise, you can put "ongoing work with Author B". If you present the work in part of a seminar, you can put "Seminar of the department X". 

But mainly, you don't have to put anything, especially if the slides are not put on the web or distributed. The only important point I would say, is to indicate if your work has been done with other people, in which case, you can write "Joint work with B".