My checked bag has been searched a bunch of times, and never, not once, has there ever been a note put in it. They do seem to like to keep locks, so I've stopped bothering with putting one on.

So far I haven't had anything go missing other than the locks, but my wife had an issue one time where they searched her bag. The TSA goon apparently repacked it so badly that when my wife retrieved her bag some of her clothing, including undergarments, was hanging out of the partially-zipped main compartment. Her's had a note in it.