Yes, use common sense in your urban hides. When someone accidentally finds it, the ideal reaction should be “it's just a nice safe Geocache”.
And it depends on the location, so check for restrictions where you intend to place it. Some state parks require containers to be transparent.
I've heard many places are discouraging the large plastic paint-bucket style (which isn't the best outdoor container anyway). But there are exceptions, where a certain container will be perfect in one place and almost nowhere else. So if you've got a very unorthodox idea, check with a local reviewer.
Thanks to everyone who has answered my question.
I made a cache container out of an old..... well, I don't want to give it away. I have never seen or heard of one of these used as a container before. So before I go through all the steps of getting it published, how do I check with a local reviewer to make sure it is okay to use?