This depends. Yes, the email address of a committer and also the email address listed in Tested-by and Reviewed-by tags is some form of advertising.
However, I also remember Linux kernel patches being submitted with lines similar to
> This development was paid for by Company Foobar

This even caused a change in the contribution policy for the Linux kernel:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/...
Quoting from that patch:
> The author may indicate their affiliation or the sponsor of the work
> by adding the name of an organization to the ``from`` and ``SoB`` lines,
> e.g.:
> From: Patch Author (Company) <author@example.com>