icons - Communicating a three stage grade of alert

In our web application there's a view where we display the stress on a hardware component.

This will be displayed with a percentage value in different colour codes combined with an icon where 100% is the expected stress rate of the component.

If the stress is <=100% the text should be green with a icon in front of it.

If the stress is >150% the text would be red with a icon in front of it.

The question is now what icon I can use for communicating a value between those values, that is 100% < X <= 150%.

It should convey an alert but of a lower grade. The text will be coloured GoldenRod so an icon in the same colour scheme would be something I'm after. I want the icon to have a differing form from the other two, so maybe something inside a square as depicted in the splash of colour above.

However I don't know that symbol to use inside it. I feel as using a exclamation mark could be confusing as it's already used in the High Alert icon.

I do realize that the use of icons combined with text is a debatable issue but the icon would be there as a substitute for users having problems differentiating between colours and thereby not gaining anything from Text Colour Coding.

Does anyone have a good idea for the icon or symbol to communicate this grade of alert? Or has anyone seen an example of how grades of alert has been communicated in other instances?

Answer

How about a green checkmark, an orange "!" in a triangle and a red flashing light (siren).
Another alternative for the red level is an "X" symbol e.g. a red octagon with a black "X" in it.

You could even add a level between the first two - a yellow "i" (information) symbol.

The checkmark makes sense for valid items, the "i" for suggestions/information, the "!" for warnings and the "X" for errors.