For example, the translation key for both the label-placing-tool and the label dialog is "Marker", which is translated in English as "Place a sign". That translation fits for the tool, but not the dialog (since the dialog shows an already placed signs content). There are two ways to look at this - either the fault lies with whoever translated this way for interpreting it too much and deviating from the original meaning (1), or the fault lies with whoever reused the key in the program. (2)
In the case (1), it would mean that we shouldn't translate a key "south-facing" with the text "(0) south-facing", since that's not a perfectly faithful translation. Even if it fits now, that might change in the future.
In the case (2), it would mean that we should try to make keys as explicit as possible. Which means "(0) south-facing" would be better than just "south-facing", and something like "rotation 0; south-facing" would be even better as there is no mistaking it.
I'm certain that a translatable key is better than a number. But since it's not committed yet and nothing else built on it, there is no harm in trying to make it a key that everyone can agree on even if it's not translated. Eg. if most people prefered to use numbers, I'd suggest a key like "--0--" since you'd get the number you wanted without translation, but could still translate it.
[Essentially - an overthought, strict version of "even if it gets translated, don't just use a bunch of random characters as your placeholder"]