Display of firearms or ammunition by dealers; security; employees of dealers

(a) No licensed dealer shall display any firearm or ammunition in windows visible from a street or sidewalk. All firearms, destructive devices, and ammunition shall be kept at all times in a securely locked place affixed to the premises except when being shown to a customer, being repaired, or otherwise being worked on. (b) No licensee shall knowingly employ any person in his establishment if such person would not be eligible to register a firearm under this unit.