Edit Recent Posts Widget

I’m wondering if someone can suggest the best way to make a callout graphic or text next to the newest news items in the sidebar on this website?

My client basically wants a red flag of sorts on the news stories as they’re added that will stay there for about a week or so to highlight that they’ve just been added.

I can muddle my way around some basic php but am mainly a designer that edits previously-created themes.

Any suggestions???
Thanks!