To use these icons (or indeed any others you fancy) for the userinfo icon on your journal/comm open up the Custom CSS page for customizing your journal and add the following to it (changing the two paths to the icon to your desired one - this code will give you Sherlock!).
Please note: This will change all the userinfo icons on your journal (not just yours) to whatever pic you choose. It won't change your userinfo icon on any other comms or journals.
ETA: The code I used originally used to work fine but now replaces all the icons (users, communities and feeds) because LJ changed the paths to their icons. The code below has been updated to fix this - if you have mini-Sherlocks (or whoever) for all your icons please fix it by using the new code.
If you do use one of them, do please give me a little credit on your profile page - thanks!