Oh you can place tracks any way but they do have an internal direction. Place two set of single track side by side
]===============> a
]===============> b
<===============[ c
]===============> d
] is where you start
> is where you end
If you use the a-b set and place right-hand signals on the tracks, you would have to rotate the ones on track "a" to get them placed correctly on the outside instead of having half between the two tracks.
Sure you could use left-hand signals on track "a" but you can't tell by looking at the track what its direction is. If you place a track marker on the track, it will point in the direction of the track but that means having track markers everywhere. This is also what the double tracks look like. Both tracks facing the same direction.
On the other hand if you always place double tracks like c-d, then there is no doubt as to which is the direction of the track. Naturally if you have left-hand running trains, you would switch the locations of the tracks.