Thanks very much, Mustang and Jonny Kansas. And, no, Mustang, my question was not rhetorical. I don't lock my phone , so no lock screen! I guess that's why I've never seen the 'charging rapidly' notification...
Doesn't show on the pulldown notification bar on my 6P. I'm pretty sure that I AM rapid charging, since I purchased the charger/cable directly from Google...but, it still would be nice to be able to visually verify that.