Obviously the layout of warning signs etc will depend on the task being carried out, but in general there is no correct layout. You need to take reasonable steps to prevent accidents and warning signs are part of those steps to preventing accidents where slips and trips are possible. Accidents can never be prevented but risks can be reduced. Even with signs out and measures in place to prevent accidents, you can still be sued for damages, but by taking preventative action you can minimise the liability/fines.
You could make a claim for tripping over a warning sign, but you would have to prove someone elses negligence, which would be hard to prove (unless you went 50/50 with the judge). If it was to happen (and thats not to say it hasnt), could you imagine the courtroom, it would be like something out of a carry on film