Entries in Registry

Hello,
While making some registry editing, I found several strange entries named "Sign.Media".
Searched the net and found nothing. Accidentally when I connected the usb stick with the "Portable Apps" on it, and clicked on "Start.exe" in the file explorer, I noticed a new such entry in the registry.
Can Somebody please explain what is it and why is it, and why it touches the registry at all.
Answers will be appreciated.
Thanks
Motim