This request can be mounted either directly onto the lavatory cistern, or at eye level on the wall above it.
On a white background it remains discrete whilst the contrasting materials will allow it to be perceived distinctly enough. Moreover, the foil is a very bright white, whereas walls and plastics are usually kept in a warmer or slightly toned white. The more vivid the background colour, the stronger the contrast of the type will be.
Please feel free to ask me for a custom-made variation in glossy white, dull black, or glossy black.