사 자 성 어
This idiom is an example of itself. This is what I'd been looking for - I was hoping there was a name for these four-syllable Chinese-origin aphorisms and proverbs that I sometimes run across and have made efforts to understand.
I found it. Here's the definition in the online Korean-Korean dictionary: "네 개의 한자로 이루어져 관용적으로 쓰이는 글귀." The googletranslate actually does a pretty good job with this (for a radical change from the norm): "Composed of four Chinese characters used in idiomatic saying."
It works the same way as the English "TLA" - which means "Three Letter Acronym" but is also an example of a three-letter acronym. In other words, "성어사자" is a four-character idiom.
Here is another picture from last weekend - a view inside the main throne-room at Gyeongbok Palace.