As part of a web-based application, we have a toolbar at the top of the page. The toolbar contains buttons that consist of small (30x30) icons with a single word underneath (for example, a search button consists of an icon of a magnifying glass with the word "search" underneath).
We have added a new button which enables users to get notifications about items that they have previously registered an interest in (if they have since changed).
What would be a good picture to use for this icon to convey the meaning of "notifications"?
Thanks for the answers, but let me throw a spanner in the works:
We already use both exclamation marks and 'i' icons elsewhere in the application for other purposes, so reusing either of them will possibly introduce confusion. Additionally, the notifications feature is not passive (like getting a new email), but requires the user to actively load them, so it really just needs a static icon.
The options we've considered so far, but don't think are particularly obvious in what they mean:
- exclamation mark
- a "warning triangle" (eg. something like this)
- a speech bubble (eg. something like this)
- a loud-hailer icon (eg. something like this)
- something along the lines of an RSS feed icon
Any more ideas?

