Do Not Apply Vibrators

I saw this on a rail car while waiting for my Amtrak ride last weekend (click to enbiggen). It reads:

DO NOT HAMMER ON CAR

Warning

Do not apply vibrators

to any part of car body

except vibrator brackets.

Use on loaded car only.

Now we all know what it is trying to say, but since I have the sense of humor of a 12 year old, it sure made me laugh. The only thing that would have made this warning better is if the first "car" had been omitted and the word "brackets" would have been changed to "holes".