So there was a very subtle, mere 3 word reference, in this week's Who episode that directly referenced 5...
"Brave heart, Canton."
it is a direct reference to "Brave heart, Tegan" that 5 used to say to her every other episode.
I love Moffat for this type of hint. Subtle, makes us old farts feel good, but doesn't hurt anybody who's never seen the reference before.