If you have a led or anything else on your computer that is controlled by writing '1' or '0' into a file, then you can use it for Pidgin notifications with the Led-notification plugin.
This plugin needs Linux.
* Unpack the package and move to the created directory
* Edit Makefile (Shouldn't be necessary)
* make install installs plugin to per-user ~/.purple/plugins -directory
If you want to install plugin system-wide for all users, just copy led-notification.so to /usr/lib/pidgin or /usr/lib64/pidgin, depending on your distro.