If you are going to ask for the tab and then just put your credit card in the check presenter without even glancing at the check, don't ask for the check, dummy. If you know you are going to pay with a card, instead of asking for the check, simply hand the server your credit card when you are ready to pay. He will know what to do with it. Don't make him make a special trip to the POS to print your check so that you can not look at it when he brings it. Bonus: doing this not only saves your server hassle, it actually saves you time--the time it would take for your server to go get the check so you can not look at it. Think about that, hmm?
Also, if you ask for the check, and your server brings it, and you look at it before putting your credit card in, for frick's sake, don't say something like, "Here, I'll save you a trip." Too late, amigo, your server has already made the maximum amount of possible trips to your table. If you wanted to let the server know that you "get it" and how generous you are to save him a trip, try giving him your credit card without first asking for the check.