Despite R.S.'s suggestions to take this "San Francisco-style Lisbon joyride", we suggest that it is not worth the excellent chance that you will be a pickpocket victim, no matter how experienced a traveler you are or how careful you are about your belongings.
NO ONE in Lisbon is surprised when you say you were pick pocketed on "the 28"! According to the Lisbon police, it is mostly Romanian gypsies who "work" at the trolley stops and the Portuguese who "work" aboard the trolleys. (Not to mention all the discomforting lighted warning signs inside the Metro stations!) We were told the pickpockets want just your cash to feed their drug and alcohol habits. There were many other victims at the station when we filed a police report. These pick pockets are known to the police, who claim there is nothing they can do about them....except to give them "a warning". They are "very smart, having practiced for 20 years".
The trolley ride was interesting....but definitely not worth the feeling of violation and the aggravation of replacing cards. (In our experience, most guest houses had no safes available for storing valuables, and larger hotels had only a few.) While our situation could always have been worse, it definitely colored our feelings about Lisbon, which I would skip on future trips. It was totally over-run with tourists....the perfect place for a pick pocket to "work"! Other cities and towns felt much safer to us....or maybe we were just lucky.
Beware any group of "tourists" waiting and crowding to get on the trolley, Metro, or anywhere else. Sometimes it is a legitimate crowd, but it is just as likely that those "tourists" are a group of pick pockets! It is impossible to be sure, when there is such a large mix of cultures and languages involved. We found it to be a sad commentary on an otherwise interesting city.