What does the little yellow "frame" icon mean?

I'm sure the answer to this is really obvious, and I'm going to say "Doh!" as soon as someone explains it to me. But you know how it is... if you can't see it, you can't see it, even if everyone else can (grin)...

In iWeb, what does it mean when there's a little icon in the upper right-hand corner of an object? The icon looks like a little yellow picture (a head and shoulders silhouette in black) inside a little dark yellow picture frame.

I can't find any mention of this icon anywhere in the online help, and a Google Images search for "iWeb icon" doesn't help.