To see the blinkies you need to be on either the Highlights or the RGB Histogram screens. In either you should see the yellow RGB blinking. You can switch between the playback image screens by using the up/down arrows on the multiselctor. It's very easy to inadvertently change the screen when using left and right to switch between images. If you no longer have those two screens available they can be turned on in the Playback Menu under Palyback Display Options.
If you intentionally over expose you can confirm the feature is still working.
I find that if you shoot RAW the blinkies start well before the RAW files actually over exposed, so I don't think the general practice of subtracting exposure is needed, and therefore marginally subtracts from image quality while also requiring additional post exposure work to add exposure back in.
