A couple people sent me some examples via pm. Thank you! It turns out that we currently can't show that a node has been edited, because the fact is not recorded in the database. We have the infrastructure in place to do so -- there is a "last edited" timestamp field associated with every document-type node -- but currently this field is not used for ordinary writeup-type nodes. (It is used for wikis and things like that.) pmdevils, take a look at the lastedit field. Patches welcome. :-)