Gunther,
whenever you plan something like a new housing for the timer, consider labeling the 2 camera ports. It happend to me meanwhile 2x that I mixed port 1 and 2 when connecting cables in the dark, resulting in my MoCo not starting. Unfortunately the surface of the housing is so rough that most stickers come off after a while and others e.g. "Panzertape" are not good for labelling.

Hi Mopperle
Not sure how much labels will help when using the timer in the dark but in the meantime you could try using a different color florescent paint around the two ports on your current timer.

Or just remember: bottom left is 1st, top left is 2nd.
Would some reminder on the display help?

Gunther, a reminder what help for sure
@Pogo007: a fluorescent paint might also be a good idea

The question is on which screen to put the indicators, so that they don't annoy...

Hard to answer. IMHO best position would be before you "Start" a process; otherwise it might be overlooked.
Thats why I think a label is the best option.
Meanwhile I bought a bunch of different tapes, maybe one of them sticks permanently on the case.

Perhapse a firmware option could be a solution. Just a separate menu when slave mode is activated. In this case on Display could be pointed to upper/lower port on the left side to select the camera release port. Whether it is stored persistent or not is worth to think about.
Regards
Markus.

I don't think I would make the slave port configurable. It just makes more sense to have it always on port 2 while the 1st camera ist always on port 1. Also I don't think it's so hard to remember, that the topmost port (when looking on the display) is the first and the bottommost port is second and thus the one that can be configured for slave.

I could add a second status screen, where I display the status for the ports, if that would help. You would then go to Status, rotate the knob to the second screen to see it.
Another option would be to add it to the "Starting timelapse" screen - but of course, this might be too late if you wonder which port is which while plugin the chords.