I run an ad all year long on Craigslist Lost and Found in my surrounding areas that says if you lost jewelry on the beach to let me know and if I have it I'll return it. Most of the time someone emails me asking if I found an item and I say no if I have not and then offer to go look for it especially if it's a recent loss. I'm also on The Ring Finders dot com site.
Also most of the local beach police, toll collectors, and some of the life guards have my contact info to share with those that lost items.