What to check before booking
If the letters are the centrepiece, ask the photobooth supplier whether their framing will suit the whole display and the group standing beside it. An example shot or a simple scaled sketch is useful if you want to compare a full word with shorter initials.
If the display works better as a separate backdrop, give each photo spot a distinct place on the layout. Think about where guests will stand to take their phones out and whether pictures taken at the display should happen independently of the booth queue.