Normal
First of all the tip is automatically charged to your sail and sign card. The charge is $10 per person per day. The envelope is for any extra you may want to give. Not sure about Carnival but Royal Caribbean leaves envelopes in the cabins and if you have the gratuities on the sea pass account they also leave little "coupons" to slip in to the envelope to let the steward, waiter, etc. know that your gratuities have peen paid through the ship. That way if you don't want to give extra $$ you still have something to hand them other than an empty envelope. We usually give more because the service is always great!
