Excellent! $$N$$ is the only force that acts upwards. So, it has a positive sign in front of it. $$F$$ and the weight $$m g$$ are acting downwards, so, they have negative signs in front of them.
• $$N - F \cos \theta - mg = 0$$
• $$N + F \sin \theta - mg = 0$$
• $$N \sin \theta - F - mg = 0$$
• $$N \cos \theta - F - mg = 0$$