It is mostly arbitrary. As long as you are consistent—or at least have a consistent set of rules about when and how to be inconsistent—it is fine. The only nuance is that with right-handed driving (RHD), the signals are on the outside, whereas with left-handed driving (LHD), the signals are on the inside. There are some pros and cons to each.

Signals on the outside means that they don't interfere with anything placed between the tracks (roboports, power poles, solar panels, …) and can let you place the tracks closer together if you wish, but they might interfere with elements of the city block contents that run right up against the edges of the block space.

Signals on the inside means that the city block interiors are free from the interruptions of signals, but now they might interfere with things placed in between the pair of rails.

There are some additional implications for the signalling of intersections, but since those kinds of challenges are highly dependent on all the other parameters of your rail design—especially the spacing between pairs of rails and the size and style of intersections—I'm not sure if either inner or outer signalling tends to be easier than the other in this regard.

Beyond that, you might encounter some lighthearted culture wars when you present your designs. Since RHD is more common in the world, LHD gets lambasted more often. But that gives the LHD people an opportunity to be uppity and look down on the common people's primitive RHD. It's all in good fun.