When you say it out loud, it sounds so obvious; but most people don't know the aesthetics of an electric fence. This is why an electric fence warning sign is recommended for property owners using this type of garden fence. The bright yellow background and bold font lets individuals know that the electric fence is activated.
Deer sense colors toward the violet end of the spectrum, so they can see blues and probably even ultraviolet (UV) light. Deer show a slight sensitivity to yellow, but tests indicate that green, orange, and red appear to them as shades of gray. We can only assume that they will have trouble seeing the sign...but it'll open up their eyes when they touch the fence. (Bad joke, but true nonetheless.)
Hang the warning sign for electric fence multiple places around your fence and/or property to warn people about the dangers of being jolted.