The hashtag tells viewers that you subscribe to the Candid Public Photography approach and it will clarify that your images are not staged or manipulated.
If I see #CANPUBPHOTO beside your images I will know what I am looking at and I will know how it was made.
You can also use #CANPUBPHOTO in your image alt text on your websites so that in time it will be possible to perform a Google image search for Candid Public Photographs.