Display protocol in Safari address bar
Solution 1:
You can temporarily display the protocol by activating the address bar with ⌘ Cmd-L and copy-pasting the current URL back to the address bar with ⌘ Cmd-C, ⌘ Cmd-V.
The protocol will, however, disappear again as soon as you load a new page by following a link on the page or pressing Enter in the address bar.
Solution 2:
Normally settings like these that aren't in the UI are sometimes available to change with the defaults command in the Terminal app. (this won't work on iOS AFAIK).
Unfortunately though, it doesn't appear there is any setting for this:
teak:~ mhp$ defaults read com.apple.Safari | grep -i protocol
teak:~ mhp$ defaults read com.apple.Safari | grep -i url
DidMigrateToMoreRestrictiveFileURLPolicy = 1;
teak:~ mhp$ defaults read com.apple.Safari | grep -i address
teak:~ mhp$ defaults read com.apple.Safari | grep -i http
I also looked through all the settings that other people have posted on the net and found no options.