When users are renamed, it is up to the user to find and replace all old instances of their signature to make sure that they redirect to the appropriate account if they want to put that much work into. The other option is the re-register your old username and redirect it to the new one. This is not feasible all the time, for instance if someone owns the SUL to the old username and comes over to take it before it gets re-registered.

I was wondering if anyone had the interest to build a tool on labs that would let a renamed user find-and-replace old signatures in an automated fashion? The tool would check against the rename log and the old timestamp to make sure it's the appropriate user, and substitute the old name part with ~~~ to insert the new username while preserving the timestamp.

I'm not a developer my self, so thoughts on feasibility and implementation are welcome. I think such a tool would be highly useful and I'm slightly surprised it hasn't been made yet.