I created a little script that looks up a random signature from an ever-growing list of quotes I have and modifies the HTML of my signature file to insert the quote into place. I trigger this script via launchd every few minutes so that my signature is 'randomized' throughout the day.
Up to Mavericks, this worked fine. Now, in Yosemite (10.10), the signature no longer gets updated. If I go into Prefs -> Signatures and drag/drop the signature from the 'All' list on to my mail account again it will trigger it to update. It also updates when I restart Mail. It appears that Mail is now caching the contents of the signature file and only refreshes it when it gets 'triggered' to in some way.
I know that there are now two possible copies of the signature file - a local and iCloud version. I've updated my script to make sure both are using the updated signature. If I restart mail or do the prefs trick, it does show the updated quote in the signature, so I know my script is running properly.
Does anyone know anything about this cache and/or how I might trigger Mail to refresh the signature with my script or some other trickery? I'm not even sure where to start looking for this sort of thing.