My thanks go to Julian Priest for these photos of a Trigger. Julian writes:
... While visiting Lisbon, Portugal earlier this month we spotted a great looking 3 wheeler that is for hire to tourists for you to take a GPS directed tour of the city. We later on even saw some tourists undertaken the tour! I've attached photos of the vehicle parked up and being driven about. Having looked at it closely it appeared to be based on scooter running gear and had a set of handlebars for the drivers controls.
Having just done a google search I've found the company's website