Abstract: A breakaway post coupling with a hollow, tubular sleeve which accomodates a ground-mounted stub post and a top, sign-supporting post. The sleeve is held onto the posts by a plurality of pins which engage a corresponding plurality of slots in the sleeve. Collars slidably engage the sleeve and force the pins into the post material as the collars are drawn over the sleeve and pins. A plurality of cutouts in the sleeve define a shear point in the coupling. When the top post is struck by a vehicle, the coupling breaks at the shear point, leaving an intact stub post upon which a new top post can be joined.