What kind of Keep Out signs are most common in our culture? How effective they are? How long is their lifetime? Centuries from now, any modern language is likely to be as hard to understand as pre-medieval Pictish. That is why verbal language is clearly not enough to communicate with the future. The impact of the message false short to function properly also in case you cannot read: this type of message is not going to scare you off. There is another kind of signs actively used in cultures all over the world.