Everyone is familiar by now with the use of yo as an attention-focusing device (Yo, be careful!). Apparently in Baltimore it has evolved into a gender-neutral pronoun; as a Baltimore Sun story says:
Elaine Stotko, an associate professor at Johns Hopkins, began hearing of kids here who say “yo” to indicate another person of whatever gender, and after pursuing survey work over two years has nailed that usage down. Now she has a paper in American Speech, the journal of the American Dialect Society.
Some examples: “Yo handin’ out papers.” “Yo threw a thumbtack at me.” “She ain’t really go with yo.”
A little further study showed her (showed yo – it can stand in for “her” and “him,” too) that this use of the word doesn’t show up in other cities; kids in Washington say “youngin'” in a general sense, but typically that’s reserved for boys.
There’s much more, including news links, at Mark Liberman’s Language Log post; new pronouns don’t come along very often, and it will be very interesting to see if this spreads.