Think of it from the point of the park officer. If they notice it, and not cover it up, then it will be read as an implicit endorsement, and will generate an unending amount of gossip and headache. Why would they want it.

The result would have been exactly the same if somebody put a bust of Hillary Clinton with letters "Clinton, 45th president of USA", even though Clinton would be a pretty safe choice for a lot of people (including those who hate Snowden).