Your device informs you when it is being charged by displaying a charging icon in the shape of a plug in the same taskbar spot where it shows your battery. By default, this icon is static.

You can have that icon displayed in a dynamic (blinking) form by editing the registry at HKLMControlPanelPower and adding a new DWord with the name “DynamicChargeicon” (without the quotes) and a value of haxadecimal 1. For those not so much into Registry Editing there is a cab available over at XDA Developers together with some other nice cabbed tweaks which will enable for instance persistent battery icon or clock, making them available in the taskbar of all your applications. Soft reset is needed to apply the tweaks.

(Source: XDA Developers)