Tested Version 4.2.5, doesn't work either.
after applying HF10 to Agent 8.5 SP1 running an ImportDataOffice.exe -E does not write back the personalized Outlook Signatures to %APPDATA%\Roaming\Microsoft\Signatures. All other files from the personalization are written back as expected.
Is this because you've got that path managed by a WSG - so ImportData can't read from the bubble anymore?
Have found a workaround for that. Running ImportData creates temporary folders in users %temp%. Deleting the auto generated temp folders after the 1st run and then run importdata again fixes the issue.