This dream is pretty strange in the sence that it absolutely, positively could be happening in my real life too. I'm working for the department at university and there's not too much to do right now so I've adopted the role of 'department's little helper', programming-wise. Also the bits about Mark corresponds the reality, apart from the goal of work.
And now the dream:

Mark, who's an international trainee from Switzerland, is supposed to be doing a system for a toilet that indicates if it's reserved or not. He has plenty of code finished already but my help is needed because Mark is going back home very soon. He don't know how to get the information if someone is in a toilet or not. Nor he doesn't know yet how to demonstrate that for the people.

So, I figured out that we could install electrical contactors into a lock so that once a lock is locked it will give a signal. You see, that's the way how locks work i.e. a metal clapper protrudes out of the door when you turn the lock. Otherwise the current cannot flow, so..

Then I thought it might be a bit funnier to get traffic lights as indicators of toilet's state. Of course we could simply set up small ordinary lights to indicate the state but a traffic light would be cool.

Having said that I started to mind my own business and Mark started to work hard with this. Again, I didn't have anything real work to do but since I've been working reluctantly the whole summer this -- my new role as an innovative force -- suited me fine.