You can learn signs by rote if you wish. Alternatively:
Most people know where the sun rises and sets. This tells you direction of Earth Rotation.
That is all you need to figure out sign of earth Rotation. If you can't figure it out, with a sketch if necessary, then there are all sorts of compass / instrument / navigation things that are going to be hard work.
(If stuck, I can tell you how to visualise this in a simple and effective way).
Once you've sussed out Earth Rotation for one hemisphere, the other hemisphere will be opposite.
As far as transport wander is concerned, the basic mechanism is the same as Earth Rotation. We have changed the angle between the gyro datum and the compass datum. How this happened is irrelevant. I.E. the effect is the same whether the earth rotated us around through space, or whether we flew round the Earth, or a bit of both.
I.E.:
Any time you fly the same direction as the Earth rotates, Transport Drift gives you more of the same (so same sign as Earth Rotation in that hemisphere).
Any time you fly in the opposite direction as the Earth rotates, Transport Drift causes the reverse effect, so opposite sign to Earth Rotation for that hemisphere.
Take that on board and you'll never need to memorise another table of plus and minus signs again! And you'll be able to recreate it from scratch should your brain dump in the middle of an exam.
CPB