I can't see how knowing which guests "pre-pay" and which guests leave the tips on their "sign-n-sail" card would make any difference to the cabin steward, or anyone else??? I can see that leaving you're gratuities on the sign-n-sail, or just handing it over in an envelope WOULD make a difference. In the latter, the cabin steward doesn't know what the amount would be,,,if any,,,and perhaps would work a little harder in hopes of bumping the tip amount up a bit. I always just leave the tips on the sign-n-sail, and hand over a bit extra when it's called for.... Seems to work for me.