I hold my hands up on this one as I don't know how to set the scope up to measure Hz?
On the tool bar you have your channel. Beside that you can select the range you want and beside that is your selected coupling. You will find it here. You have the choice of AC or DC coupling or Frequency. I think the scope has to be plugged in to have this option. And only one channel at a time may use this option.
See "Coupling control" in the users guide.
Regarding the examples given by AD. Personally I find them a poor representation. For example the 2000 Jeep Wrangler IAC has me baffled. Although I may be misunderstanding the image.
EDIT: I suspect it's a differential measurement across the two pins.