Git commit messages should be written using the imperative mood.

http://chris.beams.io/posts/git-commit/
https://github.com/git/git/blob/bca181109d6f054d525c71a84963bbdc1f0c40bf/Documentation/SubmittingPatches#L112

When pull requests are merged by BitBucket, the message starts with 'Merged in".

Question on StackOverflow:
http://stackoverflow.com/questions/30721903/is-merged-in-a-commit-message-created-by-bitbucket-or-git