I'll use a "keep back" signal on rural roads. I don't signal "slowing" much, if at all. In the city, I'll briefly signal left or right when I make lane changes or turns. I'll also direct traffic a bit to create a hole for myself if I need to merge into a busy traffic stream to get to the left turn center lane.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter