1
The movie is about a famous gangster.
To sign this, start by signing 'movie' and 'famous' to establish the topic. Then, use the sign for 'gangster' to complete the thought. Using a descriptive facial expression will help emphasize the dramatic nature of the film.
2
He dressed up as a gangster for Halloween.
Begin by signing 'Halloween' to set the context of the event. Next, point to the person, sign 'dress-up' or 'clothes', and conclude with the sign for 'gangster'. You can even add a playful, tough expression!
3
The police caught the gangster.
In ASL, it is often helpful to set up the subject and the action clearly. Sign 'police', then use the sign for 'catch', and finish with 'gangster' to show exactly who was apprehended by the authorities.