Diacritics are typographically mandatory on capital letters but you are in an obvious case where you have no other choice than missing them and use the unaccented letters. Dynamic traffic signals have the same issue, e.g.:

That should read "TRACÉ MODIFIÉ"

^{Image credits: https://www.ttsys.fr/library/catalogue/tts-catalogue-its.pdf}

It is very unlikely for it to be an issue in the context you describe. In fact, a lot of native French people were or are still taught at school diacritics aren’t required on capital letters, so won’t be surprised at all.

See anyway: Accentuation des majuscules — Accents on upper-case letters