That's the FireWire logo.
There's water under the "T" key, making it seem like it's pressed.
When you start up holding the "T" key, the machine goes into FireWire target disk mode, where it's basically just an external hard drive that can be connected to another computer.
Shut it off, disconnect the keyboard, and switch it on again. It will boot normally.
Place the keyboard on the radiator or in the sun for a day or three. If it was just water, it will likely recover once it dries out.