The rim around the bottom of the Lumax is odd for an ash tray although the wear is consistent with such a use. It is really too thick to be a lighting component so I would tend to stick with advertising ashtray.
My experience with pavement lights is that the leftover ones tend to end up to people's desks are paperweights, and one like this would be perfect for storing paperclips or loose change etc-- so they tend to see wear patterns different from those that actually saw service.
I've bought them as "ink wells" before, and various other things, but mostly "paperweights". Your worn Lumax seems to have more wear inside that mere paperclips would cause, but that's still my guess. But, 50 or more years of loose change or pens or souvenir vacation pebbles might do it-- time will wear anything down.
How thick is the "bottom" of the Lumax? To be a pavement light, it
would have to be heavy.
--ian