Abstract: A crossarm type support having a vertical post formed from a rectangular tube having a set of internal splines. A spike element molded from polycarbonate plastic resin is inserted in the lower end of the post and held in place by a pair of spring loaded pins. The post is installed in the ground by pushing on a horizontal portion of the spike element with the heel of a shoe. A crossarm is provided at the upper end formed from a second rectangular tube having a first channel along its lower edge and a second channel along its upper edge. The vertical posts and crossarm are mortised to form complementary notches for mounting the crossarm to the post. The post and internal splines interlock with the crossarm and channels to provide internal support and rigidity to the joint. The lower crossarm channel is formed to receive plastic hooks for attaching a hanging sign and the upper channel is formed to receive a set of plastic inserts for receiving an interchangeable rider sign.