How can I make a plastic tray non-slip?

I have a small plastic tray which is too smooth and slippery to put glasses or mugs on as they tend to slide off. I can't use that useful non-slip mesh as it will obscure the attractive picture on the tray. Is there some kind of varnish or something that I can brush on that will stay just slightly tacky,... show more I have a small plastic tray which is too smooth and slippery to put glasses or mugs on as they tend to slide off.
I can't use that useful non-slip mesh as it will obscure the attractive picture on the tray.
Is there some kind of varnish or something that I can brush on that will stay just slightly tacky, without actually making things stick to it?
Update: As I mentioned, I don't want to use anything that will obscure the picture on the tray. I'm really looking for a transparent varnish of some kind, or simply a way of making the very slippery surface NOT slippery.
Update 2: Perhaps a spray of some kind?
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