The restrooms are near the 200 wing of the building. They are designated with blue "Family Restroom" signs. Signage at the main restrooms provide a map showing the locations. They're marked on the university maps:
The restroom is in the basement near vending area. The restroom is marked “Shower”.
It's marked on this map.
The restroom is in the basement. Walk past Pizza Hut and Mi Cocina serving lines and around the corner.
It's marked on the university maps: http://www.siue.edu/maps/tour/pdf/MUC.pdf