It's great to see that the "Sign commit" setting is now remembered since SourceTree 2.5. However, now I'm never certain if this setting is even enabled because I'm working with a lot of repositories. So I'm still opening up "Commit Options…" to see if "Sign commit" is enabled.

My suggestion is to show an icon (e.g., padlock) next to "Commit Options…" or the commit history button if "Sign commit" is enabled. If it isn't enabled, don't show the icon.