There are various sign shops around on who’s websites you can customise your own saftey signs and hazard signs etc. The idea with these signs is that you can add an appropriate warning message for you very particular application.
They are especially handy at this time of year. For example if you were an aging rocker with a halloween fetish, you may want to warn the little dudes that were rocking up to your house in search of sugar with a cryptic sign design something like this:
I don’t know… just an idea.
But what I do know is that these customisable sign services are there to be abused. And I encourage that.