When using a visual aid in a speech, you should display the aid?

It depends on the type of the speech. If it is a short, impromptu or unimportant speech, there is no problem in displaying the aid. If it is a long, or important speech, it is better to not display the aid but if the speech is not memorised the aid should be somewhere where it doesn't draw attention and brief glances should be used if needed. Always look at the audience and not down at the aid.