A tag is probably enough, but you could also maybe ask people to put some copy about the contest at the top of each submission?Why hide stuff from newbies? They are here to see the forum, and this is a cool EA thing happening on the forum.
I would encourage people to think about this. I think the Thiel fellowship is genius - to motivated, self-driven people, university is almost solely for signalling, because they would learn a greater amount of more important knowledge more efficiently without it. A large prestigious scholarship, especially with the requirement to drop out of university, easily provides the same signalling. Since there are no fees involved, it is also much cheaper to offer (although a big dollar value is a good idea for signalling, so don’t make it too small!), and can maybe be given to more people, who can work without being constrained by the university system. People should of course be selected based on demonstrated ability to work on self-driven projects.