Excuse me, I would like to report a problem.
se-gna-LA-re — stress on third syllable. The 'gn' is /ɲ/ as in 'canyon'.
Use this to get a conductor's attention when something is wrong on the train — a broken seat, a dirty toilet, a suspicious situation, or any other issue.
Vorrei segnalare (I would like to report) — vorrei is the conditional of volere (polite). Segnalare (to report/signal) is the formal verb for reporting an issue. Un problema (a problem) — masculine, so un (indefinite article).
C'è un passeggero che mi molesta.
There is a passenger bothering me.
Molesta (bothers/harasses) — report immediately to the conductor
Ho trovato qualcosa di sospetto.
I have found something suspicious.
Sospetto (suspicious) — train security takes all reports seriously
Il bagno è fuori uso.
The toilet is out of order.
Fuori uso (out of order) — reporting a broken facility
Italian train conductors (controllori) are the primary point of contact for any issue on board — they carry radios and can contact the train manager (capotreno) for serious problems.