Personally, I wouldn't care about having an icon at all, so much as just having sycned history in general, but for those who want the distinction, I think this would suffice. If you really wanted more clarity on where the history item is coming from, you could have a little desktop icon for when you're looking at synced history items on mobile, and a little mobile icon on synced history items when viewing history on desktop.
Now, if you're using Orion on multiple desktops/mobile devices, I'm not sure how you would distinguish that... but I feel like my suggestion is enough, at least as a start.