Abstract: A crossarm type support having a vertical post formed from a rectangular tube having a set of internal splines. Spike elements formed from flat steel stock are bolted in the lower end of the posts. A plastic stabilizer block is inserted between the spikes for strengthening the base of the post. The post is installed in the ground by pushing on a horizontal portion of a spike with a heel or by the use of a hammer or the like. A crossarm is provided at the upper end formed from a second rectangular tube having a grooved channel along its lower edge and a slotted 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 receives hooks for attaching a hanging sign and the upper channel includes a plastic insert for receiving an interchangeable rider sign.