Usually a theater will display it on the screenings billboard.

"Superman Returns - 3:00, 3:45, 4:15... etc"
"Superman Returns DLP - 4:00, 4:30, etc..."

Also... Fandango will tell you if the theater you are heading to has DLP screenings.

what's up with Landmark theatres and their supposed DLP screens? are there systems already in place and just showcasing 'non-film' engagements: Saraband, Bubble, et,al? If so, they are not doing a good job promoting them or with DLP.com proper, I didn't really get the sense that smaller independent distributors/studios had the budget to release films in 'digital'/non-print form.