These twin stone towers still mark the entrance to Straitsmouth Way in Rockport. In the image below, you can see the Google Street View perspective of this same scene as it looks today.
“Stone Haven” was the name given to this part of Rockport, stretching from the South Street entrance to Straitsmouth Way and continuing through to Gap Cove and Gap Head Road. There is still a Stone Haven Lane off of Straitsmouth Way.
Until I started researching this postcard, I’d never heard the name Stone Haven used to describe this section of town. All the references I’ve found to it date from the early 1900s. For example, the 1908 book, Who’s Who Along the North Shore, includes this description of Rockport:
Rockport is a town of 4500 population, has a post office, and a railroad station on the Gloucester Branch of the Boston and Maine railroad. Electric railway to Gloucester, Pigeon Cove and Lanesville. Localities, in the town: Pigeon Cove, Ocean View, Stonehaven, Lands End.
Similarly, the 1907 Massachusetts Year Book and City and Town Register describes Rockport as consisting of five villages: Rockport, Pigeon Cove, Ocean View, Stonehaven and Lands End. And the 1919 Alphabetical List of Unincorporated Villages and Sections of Cities and Towns published by the Massachusetts Bureau of Statistics lists Stonehaven as a section of the town. Also, The North Shore Blue Book for 1912 lists the address of the Straitsmouth Inn as “Stone Haven, Rockport,” and lists the address of a summer resident by the name of Oril Arnes as Stone Haven Cottage on Stone Haven Rd.
The earliest reference I could find was in an 1896 magazine advertisement for product called Eureka packing. It featured a testimonial from one H.A. Twichell, whose address is listed as “The Stone Haven, Rockport, Mass.”
This postcard was published by E.C. McIntire of Gloucester and printed in Germany. It has no date, but is definitely from before 1917. Judging by how its markings compare to other postcards from this same publisher, it is probably from somewhere between 1910 and 1915.
[Note: Since first posting this, I found another copy of the same postcard with a January 1911 postmark. That means this is from at least 1910 or maybe earlier.]
Vintage Rockport 
With the name “Stone Haven” and the two pillars made of rounded stones I had to do a double take. There is a very similar setup at the intersection of Haven Ave where it comes up to meet Granite Ave over in Pigeon Cove.
http://g.co/maps/w8aje
But I guess there are quite a few piles of stones marking streets from that era.
Great website. If you ever find a postcard of the house Eben B Phillips built on the corner of Haven Ave and Phillips Ave. (1877) You have postcards for pretty much everything else that was built on that Avenue.