Currently, it seems that the sourcetree:// scheme supports only the following:

• checkoutRef
• cloneRepo

Although I was unable to find the protocol anywhere online in order to know for sure, testing various URLs failed to show a way of simply opening/viewing a local repository (or bookmarked repository or working copy) in SourceTree.

I also submitted a question to Atlassian Answers (see link below), and in fact I am raising this feature request at the suggestion of the responder.

(As it happens, I eventually created my own custom URL scheme that opens a local repository in SourceTree, but still it would be nice to have it supported natively.)

More details here:

https://answers.atlassian.com/questions/277682/does-sourcetree-openrepo-or-similar-exist