I did a test implementation of this (mostly I copied it from my existing one)
You can get it at http://www.cratchit.org/download/OpenNTF_ME_SecureIcons.zip (3.80MB)
I updated the icons, it looks a lot better than before, and all the elements are combined in to one spot. Instead of separate lock, cert, etc, it combines certificate, envelope, and key elements into one displayed icon.
Here's an example with everything turned on: http://www.cratchit.org/Images/OpenNTF_ME_with_SecureIcons.png
Changes are:
Added (secure_icons) subform.
Added Image Resources (all that begin with "CERT_")
Modified Memo, Reply, and Reply with History forms to add computed subform that calls "(secure_icons)". The only reason this is a computed subform is to keep your forms from looking icky in the designer.
You'll want to triple-check my hide formulae on the subform. This mod has been working for me in both R5 and R6, but I might not be using it to full potential. Also, you will NOT want to refresh from this template, as I did this in R6. Just open it in designer and copy the elements over. Or you can just open up the template, click "New Memo" and play with your Delivery Options to get a feel for it. The pertinent options are Sign, Encrypt, and Prevent Copying.