The following resource pack replaces the oak sign model with the acacia sign, birch sign, bamboo sign and cherry sign models depending on the sign's rotation:
incongruous-signs-demo.zip

Download and apply this resource pack, then place oak signs on the floor at varying angles. It'd be expected that the sign displayed in the editing UI would respect the sign model used in the world (rotated accordingly to be correctly forward facing), however this is not the case and the acacia model is always used.