Summary

Yes, you can refer to Bitbucket Cloud issues, requests, and users directly from a comment on an issue, or a commit message.

Automatic Links

When you create a reference, saving the comment (or issue) causes Bitbucket to automatically link to that object. You can also mention an individual account or workspace — even insert an emoji. For items that are repository-specific, such as issues, pull requests, and commits, references to Bitbucket objects always refer to the current repository. 

Refer to Mark up comments to see specific examples of linking to Bitbucket objects from Comments and Commit Messages,