I had heard it said that this existed, but today, I got a picture of it: Upper Midwestern dialect graffiti. It's on the Wisconsin campus in Madison: Ya hea!
Well, OK, the author was not a good speller (though you gotta give'm slack on this -- it ain't in the dictionary). But sadly, maybe it's not dialect graffiti at all: Could be an effort to write 'ya hear?' with a marker that was running out of ink.
I'm sticking with the first version.