FFF: The TI indicates rate of yaw whereas the ball will indicate centripetal force; the ball is useless in a spin. You don't need a mnenonic, just remember the standard spin recovery - especially the bit about "full rudder opposite to the turn indicator".
This is a bit worrying:
I've never looked at the instruments during a spin
- in an aggravated accidental spin you may not get the direction right just by looking over the nose - you MUST look at the TI and then apply the appropriate rudder.
A TI will indicate correctly whether inverted or erect but a TC will probably tell porkies when inverted because it's designed to be slightly sensitive to roll rather than just yaw. HTH
HFD