A highlight of the Purim celebration is the public reading of the Book of Esther. Unlike many other Jewish communities, in the S&P tradition the Megillah is not read according to the ta'amei hamikra (cantillation marks). Instead, it is read in a fixed recitative which, attesting to its antiquity, is virtually identical across all of the communities within the S&P tradition. You can listen to some examples below.
There is another unique custom in S&P congregations: while other Jewish communities respond to each mention of the villain Haman by making noise, often with rattles, in the S&P tradition this is actively discouraged. For instance, in 1783 the Mahamad of the Spanish and Portuguese Congregation of London ruled that anyone causing a disturbance during the Purim service was to be evicted from the synagogue. Even on Purim, the values of gravidade (seriousness), decorum, and dignity of the prayer service are maintained. The quiet atmosphere also helps ensure that the entire congregation can fulfill its holiday obligation of hearing the entire reading.