No one likes to be told "no." Whether it was your mom telling you that you couldn't have the latest toy when you were a kid or your boss saying you can't have that raise, "no" is usually not a word that evokes positive thoughts. So, why would you put it in your store displays?
Many stores that sell fragile items will have signage accompanying them that read "Do not touch" or "No touching" or "You break it, you buy it." These signs not only cause a negative reaction in the customer, they are plain rude.
If you feel your merchandise needs a warning, be mindful of how you phrase it. "Please handle with care" is a polite way of getting the message across, but even better might be something like "We would be happy to assist you with these fragile items." A sign like this encourages customers to engage with store clerks, offering more opportunities for you and your employees to woo them with stellar customer service skills.
Your employees can be polite and your store welcoming, but if you have negative signage on your display tables, you might be sending the wrong message to shoppers.