OmU
Short for "Original mit Untertiteln" (original with subtitles). The film you are about to watch will be shown in the original version with German subtitles.
OV
Short for "original version". The film will be shown in its original language without any subtitles.
OmeU
Short for "Original mit englischen Untertiteln" (original with English subtitles). The film in question will be screened in the original version with English subtitles. Or French subtitles (OmfrzU) or Arab subtitels (OmarabU) ...
DF
Short for "Deutsche Fassung" (German version). The film you are about to watch will be dubbed in German.
No version code
This one's tricky. Mostly you will be faced with a German film in its original German language with no subtitles. But sometimes, especially in rural areas where films are usually dubbed, this might also connotate a dubbed version. If you do not find a version code, assume the film is in German (or double check with the cinema).
We hope this helps! Enjoy your Eurotrip!