You didn't copy-paste it correctly.

Putting it in a file as suggested will work. But in looking online, it seems to me that Ctrl-D should signal end-of-file on OSX. I don't know why it's not working. I've never used a Mac, though. Can anyone who does use OSX share their experience?

The warning about the signature not being valid is because you didn't do the lsign stuff that I mentioned in the guide.