I have no signal here.
Stress 'SE-gna-le'. The 'gn' = 'ny' sound.
Use this to explain to someone why you couldn't take their call or why your connection is failing. Also useful when you need to physically move to get reception.
'Segnale' = signal. 'Non ho segnale' = I have no signal. 'Copertura' is the more technical term (coverage). Related: 'zona morta' (dead zone — no coverage area), 'campo' is the informal word for signal strength ('ho poco campo' = I have weak signal).
Ho poco campo qui.
I have weak signal here.
Colloquial 'campo' for signal.
Sono in zona morta.
I'm in a dead zone.
No coverage whatsoever.
Esco fuori per chiamarti.
I'll go outside to call you.
Moving to get better signal.
Italy's metro systems ('metropolitane') are gradually installing underground mobile coverage, but many older stations still have none. Milan's MM (Metropolitana Milanese) has the best underground coverage. The universal Italian excuse 'ero in metro' (I was on the metro) is so commonly used to explain unanswered calls that it has become something of a cultural joke.