Let me demystify a few common ones:
Safety First - This is a dangerous environment and we employ people who make mistakes, sometimes often. We need to shock them out of complacency to reduce errors.
Quality related material - The company's employees routinely cut corners and need to be reminded to be careful and take their time.
Do Things Right The First Time - Speaks for itself, lots of re-work happening.
Didn't need nearly as many of those posters years ago.