I came up with lots of ideas, but they were either a lot of work or not quite right. Sometimes the simplest idea is the best. This is what I decided on:
I found picture frames at our local closeout store 12X22" for sale, 2/$.99...fantastic!! They're even painted a nice silvery color-which is kinda Mexican. (I bought all 12 of them, BTW.) Then I bought a roll of galvanized hardware cloth with 1/4" mesh...
I cut the hardware cloth 1" larger all around than the picture frame opening...folded the excess in like a hem and stapled it inside the picture frame.
I scattered the lanyard clips evenly and hooked them to the metal mesh so they could hang down; stuck velcro on each corner and its ready to install! I'll take this to the restaurant tomorrow, attach the other side of the velcro to the underside of their shelving, and it's done!
The jewelry will hook into each of the lanyard clips and will hang about eye level--perfect to catch the eye. To examine closer, the hostess will have to unhook each piece which needs two hands-easy enough but impossible to just grab and walk off with.