On Tue, 08 Aug 2017 16:41:36 -0700 James Bottomley
> The rule, I believe, is that only the person who transforms the email
> to a git tree should be the last signoff in the commit log, even if
> they're a tree pulling into another one and thereafter the signoffs go
> in the merge commit, so the signoff sent by me in the signed tag when I
> send the main tree to Linus is my signoff for transmitting all the
> commits, which includes the rebased ones in this instance.
According to Linus:
"Rebasing really is pretty much the exact same thing as
applying a patch."
And so should have a Signed-off-by from the committer.