prosperous, bright, clear
昌 centers on flourishing light and clarity: something prosperous, bright, and clear. The meanings grow from the image of a sun shining strongly and spreading its influence.
昌 combines 日 (sun) with 曰 (to speak), suggesting the sun speaking forth light and prosperity. The idea of bright flourishing is well established.
Two suns 日 stacked together, with the lower one speaking 曰 its brightness upward. The double sun makes everything prosperous and clear.
For ショウ, imagine a prosperous show under two bright suns: show -> ショウ, and the stage is brilliantly lit.