In my opinion it's the absence of a coloured bitmap. First open your letter-bmp as alpha-file and then use the fill colour button
at first I want to thank you for your input. To be honest, I do know scrolling Displays on buses in real life but I didn't give it a try in script. This is, as you state, due to the performance problem for which I wasn't able to think of a concept against. I didn't want to move the pixels on the texture, much more I thought about moving the whole texture around the face. Like the OMSI-rollerblind-movement with fixed increments instead of a smooth animation, but in x-direction, not in y. For fixed line numbers I thought about the use of transparency and a separate texture layer. Since Marcel Kuhnt (not only the first name, that's another user) implemented the rollerblinds in a special material kind, I didn't give it a try yet.
As for the smoothing effect, as I use a texture of a 8 times higher resolution in each direction: I quite like that effect, since in real life the lit LEDs do reflect on their turned off neighbours. Also keep in mind, I've increased the effect of the night texture on the result in the settings of the materials while keeping the "LED-texture" quite dark so you see the written text much brighter in a darker environment than in a lighter one but it still would be readable.
with normal night map effect it would look like this:
(the upper and the lower textures. I didn't reset the prep-material for the middle texture)
On top of that in reality the dots of, at least LED displays, might be a bit smaller and more spread than on my script. I've seen displays where the spacing of the LEDs is two or three times as wide as one LED.
Additionally I think this smoothening effect isn't that big of an issue, since in the simulation you won't see this texture directly, there's always at least a layer of "glass" in front which as well affects how it looks. Secondly you mostly look at the vehicle at a whole and don't get that near to the destination display. I hope you at least don't look that close when driving the vehicle Although I spend a lot of time with that stuff I'm quite sure that most of the users want to look on the road and not at their destination sign.
Never the less I really appreciate beeing not the only one having those thoughts,