Opposite an overcall of 1NT, we play "systems on", so that:
1C - 1NT - P - 2H
the 2H is a transfer to spades.
But how about this situation:
North deals and opens 3C. Partner (East) bids 3NT. Now, as West, I had a problem. Are transfers on, or off in this situation? This is the bidding:
3C - 3NT - P - 4H
Is this a sign-off in hearts, or a transfer to spades?
I decided that discretion was the better part of valor, and passed. Partner played 3NT beautifully, squeezing South in diamonds and spades to pick up 10 tricks. But there are 11 tricks in hearts, and so it was not a great board.
Once you are playing "systems on" after NT overcalls, Stayman and transfers should be on over a 2NT or 3NT overcall as well. On this hand, though, I have an even better bid available -- I could have bid 4C to cater to partner having four spades. Since clubs is North's preempt suit, this would be unmistakably Stayman. I simply was not thinking.