To recover your old ProBoards account, you need to request password recovery on this forum using your display name (the one that is shown on your posts). You will then get an email, be sure to check your junk email folders.
Join the IRC at #frutiger-aero-archive on LiberaChat for any account-related inquiries or contact the admin at daniele63web@hotmail.com.
If you have registered after the 7th of November or have never posted, you need to re-register.
I use it for RSS Guard which also has an RSS-themed shield icon, but more so flat design. Icon Archive, the site that has it, lets you download it in ico, icns, and png formats.