When the mouse hovers over most icons in the general vicinity of the omnibox, a tooltip appears to briefly explain what the icon does.

The icons for bubbles do not. e.g. "This page was prevented from setting cookies" (IDS_BLOCKED_COOKIES_TITLE) and "Allow foo.com to open all web calendar links" (IDS_REGISTER_PROTOCOL_HANDLER_CONFIRM)

The icons are small and usually non-obvious as to what they do. Users may avoid clicking them because they don't want to accidentally break something. Tooltips can help them understand what the icon actually does.