<p>I hope this method is correct:
There are 3 forces on the sign, gravity, A, and B. The sign will have to be in equilibrium so we want the the net force to be 0 and all the forces to balance out. Instead of using the 30 degree angle, instead use it’s complement of 60. The y-component of the tension is just the weight. We know that Ty = T sin 60 so we can easily solve for the tension of A, 500sqrt3. Applying the Pythagorean theorem, we can solve for Tx, which is 433 N. This should also be the tension in B as well. So 433 N. If I’m wrong, hopefully someone can correct it.</p>