What are the icons for thread notifications supposed to be? "New Messages" looks like a tiny dragon or lizard breathing a huge gout of flame, "No New Messages" like a potato-patterned round shield with a red border, "Closed Thread" like an earthworm and a mealworm stuck on the hook of a spinnerbait lure, and "A Notice" is obviously a scroll.

"Closed Thread" looks like a misshapen sword with antlers.

Fire breath
Bunker shield
Sword in the ground with a long flag waving in the wind
Scroll

Closed = rock?
New message = flame strike
Closed = crossed swords
Notice = scroll

This message was deleted by the user at 03:55, Thu 17 July 2014.

I got on a smart phone an zoomed in

New Messages = a stream of flames, looks like fire breath
No New Messages = Is a bunker style shield
Closed Thread = is a sword with a long banner/flag in a ribbon like shape that is tied around the handle
A Notice = is yah a scroll

use the magnify option on your computer if your on one, if your on a phone just zoom in yourself.

Well, the New Messages icon is definitely a flame of some kind, meant to indicate that the thread is "hot," or active.
The No New Messages icon is a lot trickier. I'm not going to venture a guess as to what it is or what it means.
The Closed Thread icon, well, it's clearly a dagger. I've always seen that the dagger is stuck in something, such as a table, or someone's back. I like to think that the dagger is stuck in the back of the thread, meaning that someone came along and put an end to the thread--once and for all.
The Notice icon, is, of course, a scroll. It's essentially pinned to the door of the game/forum, which was common practice in medieval settings. It symbolizes that the notice is put it a place where everyone should see (and read) it.