If that was on a single decal, it would not be any more difficult than the sideways spelled name.
Since it is black text on white background, it should be quite easy to make a decal using laser (or even ink jet) printer on a clear decal film.
Either way, unless the post is over scale, this will be really tiny print.
I'm just saying that there is probably already a single decal that fits the bill, even if it is in some other scale (Z. T, ?)
That is certainly easier than trying to cut tiny letters apart and separately align them in a vertical orientation. And using an available decal is still a lot easier than making a custom decal.
I wonder what other railroads put their names on crossbuck posts, and if they all turn them sideways where the do that. Fortunately, I never saw one around here for the railroads that I model.