On a lunch break from his sales job at a construction company in Illinois, Steve Kovacs walked into McDonald’s , where he saw a picture of a chicken sandwich on the digital menu. When his time to order came, he pointed at it. But the sign had flipped to a new screen and he was now pointing at a burger.

Mr. Kovacs, 43 years old, couldn’t remember the name of what he wanted, and with 20 customers behind him, he just got the burger. When he finished eating it, the McDonald’s menu flashed back to the chicken. Mr. Kovacs bolted up and ordered a Hot ’n Spicy McChicken.

“I got my Quarter Pounder, but I got excited for that chicken thing,” said Mr. Kovacs.

Digital billboards are now everywhere, and companies love them. The only problem: people have a hard time reading them.

Many establishments have replaced older, static menu boards with dynamic, high-definition screens. The screens let restaurants flash seasonal promotions to guests, advertise for sponsored movies, and create a more lively experience in line, restaurant consultants say.