jiggawagga

I'm completely new to modding MC, but I have an idea I'd like to try out for a little racetrack I put together on a friend's server. I've looked around the different MC Forge tuts and think I have a basic understanding of how it works. I'd like to make a simple sign block that when you right click it, it starts a timer, when you right click again, it stops, and a third time it resets the time. I know how to write the logic in Java, but what I'm wondering is if I can just inherit from the existing Sign block when creating my new block and then just override the right click method to do what I want it to. Along those same lines, would any block be extensible if you knew the name of the block?