Julianne Moore wears a gold necklace with the letters L O V E arranged in a square shape. The necklace is based on LOVE, a sculpture by American artist Robert Indiana. It consists of the letters LO (with the O canted sideways) over the letters VE. The image was originally designed as a Christmas card for the Museum of Modern Art in 1964, and first exhibited as a sculpture in New York City in 1970 (source: wikipedia).

The O in the movie necklace is canted the opposite direction, compared to the original sculpture.

A similar necklace is available at quixotic-inc.com.