This question is a little weird and dependent on the situation, but I think your answer will be the second one.
Signs won't really help you unless you are actually looking at them while driving. Just having a photograph and sending it to someone probably won't help them, since you could just tell them what's on the sign that's important. You typically don't stop to take a picture of the I–275 sign rather than just telling them to get on I–275. Also, signs, especially for interstates, can be all over the place along the road, so it may be hard to decide which one was photographed while driving. TL;DR, it just doesn't make much sense to photograph a sign to give directions.
If you want to avoid photographing the landscape, then... don't photograph the landscape? You don't take pictures of signs purely for the purpose of deliberately not photographing a landscape. Just shoot somewhere else where there isn't a landscape.
The second one makes the most sense. When you're taking a road trip, one way that you can indicate that you're entering a state is by posing by the "Welcome to Georgia" sign or its equivalent in any other state.
Since the first and third answers are out, it's obviously not the fourth. I think the second one is your answer.
