Inflamed over sign that says 'Flammable'? And does 'slim chance' and 'fat hope' mean the same thing?

Here's a poser: what do these two signs mean?...

I suppose, by showing these tell-tale warning signs, I would not have presented a poser. You would likely have guessed that they mean the same thing, ie, the material in question can easily catch fire or even explode. But why not just catch someone offguard and ask that person what's the difference between flammable and inflammable?

I once wrote an article on these two words and others like valuable/invaluable under the rubric "confusible words". More recently, an interesting article in the Huffington Post elaborated on the history of flammable versus inflammable:

Flammable or Inflammable

http://www.huffingtonpost.com/william-b-bradshaw/flammable-or-inflammable_b_3212693.html

My little bit of present research was instigated by something Nick sent me: an article on so-called "contronym" words:

14 Words That Are Their Own Opposites

http://mentalfloss.com/article/49834/14-words-are-their-own-opposites

Finally, a little bit more online research led me to this forum site with a rather provocative header, "English: The Language of the Stupid"...

http://www.davidicke.com/forum/showthread.php?t=228527

At the very least, the site above has these two humorous posters: