This plugin was made at the request of LordOfPex on the Bukkit Forums, the post is here.
This plugin looks at every sign being made, checking to see if it has the [essentials] tag at the top of it. If it does, it'll check to see if the user actually has permission, and if they don't, it'll actually break the sign and alert admins.
As outlined on the forum post, you may want to give some of your users access to coloured signs, but in doing so, you open up Essentials' buy and sell signs (which can then be exploited).
None.
signfix.notify - Users who have this permission will get notified when an Essentials sign is made, but the user was denied.
signfix.bypass - Users who have this permission will be allowed to create Essentials signs as per usual.