iKnop's documentation is 100% in Russian, but I tried it (only) because it's available from the Safari Extensions Gallery.
I couldn't figure out how, even if, it works.
Admittedly sparse, but here are the English provided instructions:
"This extension greatly enhances the addition of visual bookmarks in your account. Add visual bookmarks from the page that you want to add, select the icon for the bookmark, and click Create."
I take this to mean you have to have some icons from which to choose. These could also be found with a web search.
Having not tried the extension, it's not clear to me if it replaces the text/name of the bookmark with the icon or appends the icon to the name.