While browsing sites using the Android app, I came in a question I happen to remember being closed. From the question list view, there is no indication that the question is closed. The title does not bear the usual
[on hold] or
[closed] markers. Starting in 0.1.24 the question itself now includes a fixed banner at the bottom of the screen indicating the question is closed and abbreviated information about why. The interface for this is quite clean, but you still have to be in the question view in order to learn this.
Edit: The on-question banner is still too subtle. It should be at the top of the screen and yellow as in the main site rather than at the bottom and grey. Also as of the latest version there is still no indication whatsoever of closed questions in the question list.