If you still have Panda Antivirus installed, you must not remove those files ofcourse
Here you can find what is known about Avast detecting infections in Panda files:
You can delete them from the Chest, but the location you give for the original file location is a windows protected folder used by System Restore so I would also recommend that you disable system restore, reboot and scan to ensure that your system is clean, if so then enable system restore.
As you say the pav.sig stuff is not a virus, but the signature of the virus file. I would stop using PAV’s online scanner and remove it from your uninstall/system and use one of the other online scanners scuh as Trend Micro’s Housecall, this at least encrypts its siignature files so they don’t cause false positive hits.