GitLab(9.5) recently introduced GPG commit verification. On Ubuntu 16.04.x gpg2 is installed and can be used instead of gpg which is in the latest docs published for GPG with 9.5 release.
So you have github or bitbucket account and repositories setup already. But the problem is if you did not set the user name and email on your machine, most probably you will see Author not mapped with question mark sign.