it is called "http://elderscrolls.com/games/morrowind_armor.htm" because most ordinators are from House Indoril.
Regardless, this is the closest thing we have for a symbol for House Indoril. It might as well be, since the devs chose to use that hand symbol for the Tribunal expansion as well. With Indoril being the most conservative and religious of the five Houses, it would logically follow that their symbols would include more religious references than most of the other Houses, so this might as well be a symbol of Indoril. It could believably represent House Indoril.
The symbol on the cover of Morrowind is the Septim dragon seal, and has nothing to do with the temple.
It might not be their official symbol or anything, but it's quite clever when you think about it. It combines the diamond that is used by the Dunmer people a lot, and incorporates a symbol of Akatosh, the Dragon who was broken when the Tribunal became gods. Maybe I'm reading too much into it, but you could easily say that symbol represents the Tribunal or their Apotheosis from a certain point of view.