It's not the 1990's any more.
Hi-Tech Removable Adhesive Wall Signs for Industrial Facilities. They stick to anything and are SUPER EASY to apply. You will be amazed.
They stick to Cement Block, Steel, Floors, Walls, Doors ... Anything Dry. They are Waterproof, Highly Durable & Long Lasting. The adhesive is like an industrial grade Post-It Note™ - Permanent forever but easily removed.
They will not damage your walls.