Mothers, does covering your child's mouth work?

If she is 3 she is old enough to understand "use your indoor voice" I have always just said in a low tone while putting a finger to my lips "shh, use your indoor voice" I wouldn't cover their mouth as it would probably provoke a feeling of anger from the child and I think my way is more effective and teaches them in a better way. It teaches them yes, they can talk just more softly than they are now. Your way would seem to suggest they aren't allowed to talk at all and isn't appropriate.