Early 20th Century Miami Beach Postcard

Is There Even One Square Inch of Deserted Beach in Miami Today?

This undated vintage postcard of Miami Beach shows a beautiful, undeveloped stretch of tropical Miami Beach. The windblown palm tree and the whitecaps in the water, speak of a blustery Miami winter day, or perhaps a gathering storm. The black-and-white image illustrates just how much can be done with the photographer's eye while not resorting to the retina-searing bright colors used on postcards today. This example was found in a trunk of items belonging to my great-aunt Edith who died in the early 1920s after contracting the Spanish Flu in 1919 and never fully recovering. I'd guess this is from the 1900-1910 period.

On the back of the postcard in the upper right corner, is this stamp placeholder. I've googled for an hour trying to figure out what the "A Z O" surrounding the "Place Stamp Here" type means, but to no avail. Any ideas?

U P D A T E :  Loyal reader Annie has solved my newest mystery! The AZO is a paper mark, which now can be used to date unpostmarked cards like this. According to the listing, AZO with two triangles pointing up and two pointing down, date this card to the 1918-1930 period. Now I'm guessing that my grandfather might have purchased this for his sister. He was in boot camp in Georgia during 1918, and could have bought the card at that time. Here's the site Annie found. Bookmarked and added to my "Reference" list.