As an American I am not sure if we could really pick out a Portuguese accent as there is not a large Portuguese community here. There are some Portuguese enclaves in New England, especially Rhode Island and Massachusetts but an average American watching TV or listening to the Radio would hear a Portuguese accent as roughly Spanish or Italian.

If you are talking about Brazilian Portuguese, one distinguishing feature is they way they say the word 'Brazil'. Brazilians pronounce the name of their country 'Braziw', as if it had a 'w' at the end. Everyone else pronounces the 'l' at the end. If you hear anyone say 'Braziw', this is complete give-away that you are talking to a Brazilian.