What name was given to McDonald's logo after the arches were combined into an M?

The combined M-shaped McDonald's logo is known as the Golden Arches.

The name comes from the large yellow arches that originally formed part of McDonald's restaurant architecture. In the 1950s, many buildings used arches as prominent roadside design features, making the restaurants visible to passing motorists.

In 1962, the two arches were brought together into a stylized M for the corporate logo. The mark retained the architectural association while becoming much easier to reproduce on signs, wrappers, advertisements, and other branded materials.

The term refers both to the physical arches and to the logo derived from them. It is not simply a nickname for the letter M: the visual idea depends on the arches' architectural origin and their golden-yellow treatment.