Student or Learner
"Sharp Objects are Strictly Prohibited!"
"Corrosive & Flammable Items are Strictly Prohibited!"
The above warnings are put up in our school!
Are they naturally written? Should I replace "Items" with "products or materials" or something like that?
Should I add "in this area" at the end of each warning?
I agree that "Materials" is a better choice than "Items." Use "or" instead of and."
"In this area" is self-explanatory. You don't need it.
You can also just say
NO sharp objects
NO corrosive or flammable materials
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.