The forums software itself documents post edits, either by user or mod/admin.

You can see the post in question https://bitcointalk.org/index.php?topic=47811.0 is untouched, otherwise the date line would be underlined as in this post which i have edited after posting for demonstration of the function.

The only way to do an edit that is not noticed by the forum software would be by directly modifying the post on the database level.

EDIT: Ok, the function showing that a post was edited doesn't seem to be working as it should. You may now start going paranoid.

EDIT2: Now it works after the 5 minute grace period.