You are
Exclamation mark
I am short and I always exclaim
It is just one character long
I vary in appearance, but only have one name
You can have different fonts, but it's still called exclamation mark
I am silent, but in your head I make sound
It makes no sound but when we read it, we imagine emphasis
I am intangible and often bound
It has to be bound to other words
I often come with colors,
And always with shapes and lines
Different colors, fonts, etc
I serve two purposes
Of which one of them is to please the eyes
Exclamation mark has its own purpose. The one to please the eyes can be some sort of notification you were expecting