IDIOMS

arm candy

(idiomatic) An attractive, seemingly romantic companion who accompanies a person in public simply so that one or both of the individuals can gain attention, enhance social status, or create an impression of sexual appeal.

Example: 1992 Aug. 21, Marcia Froelke Coburn, “Marilyn’s enduring appeal”, Chicago Tribune:
  All About Eve (1950, FoxVideo). [Marilyn Monroe had] already had mini-roles in eight movies when she turned up as George Sanders’ arm candy in the party scenes of this film.
2003 Feb. 17, Jeffrey Ressner, "Shot on Location," Time:
  Friends described her as always ready to serve as "arm candy"—that is, a pretty date—to industry players, in hopes of landing a role.