According to the articles, what should be displayed on or near the main building of every public institution?

U.S Flag

Explanation:

According to the Department of Veterans Affairs, Office of Public Affairs, the U.S. flag should be displayed in every public institution's building. It should also be displayed near schools and in polling places during elections. State holidays and national holidays should be the days when it should certainly be put up.

U.S flag should be 'hoisted' slowly and should be lowered slowly and ceremoniously. One should never disrespect U.S. flag  and while hoisting or folding it, should not make it touch on the ground.

this would be in the imperative mood. it is a category of verb forms that are used to express orders,instructions,commands or requests.