No idea; it's an older feature copied by OpenSUSE from kdepim.
Any way to trace that history? The icon must do _something_.
I tried an https site. The lock icon appears but I did not see the receptacle icon do anything.
Clicking on both the lock and filter icons produced dialog boxes. Nothing with the receptacle icon.
BTW, when I tried the https site I got clobbered with oodles of certificate questions.