Ya' know whats funny is on my Laptop and my Work Computer only the top half of the postcard shows - for the life of me I couldn't understand why you'd post a picture of a bridge in Florida

Anyway, on the home desk top I can see it....
This is interesting - A Miss J. Herreshoff (note not MS.), postmarked 1929....likely that she is one of the Herreshoff Nieces:
Jane "Jeannette" Brown Herreshoff (1876-1964), daughter of James Brown
Julia Ann Herreshoff (1864-1942), daughter of Charles Frederick.
No Idea who Martha was...