For the Enterprise A they added the little rectangular and circular shapes that were on the original TOS model's underside to the movie model, most people's versions of the ship will have this present, they are behind the 4 underside phaser turrets, an orange circle with red outline, a compound shape of 2 rectangles touching perpendicular to each other in light blue with a slightly darker blue outline around that, then a light grey rectangle with blue outline and finally a grey square with red outline, they appear to serve no function whatsoever and were probably just added as nostalgia on the part of the model guy who had to repaint the ship.