Do retirees need to sign out/sign in on Transition Leave?

Retirees do not sign out or in. If you are going on transition leave you are not yet retired, so you must sign out. Once you have retired you no longer are on leave so there is no need to sign in.

Kind of, as you sign out of the duty station in a way when you clear.
You should clear prior to terminal/transition leave (at least in the Army). My leave form was just there to exist as a record for the finance department for what goes when for pay

I think I did, but that was in 1976.