Yes, this is the sign.
- The "No Trespassing" sign in the background is meant for the forest adjacent to the road; not the road itself.
- The Title 31 definition of "Private road" is to be interpreted as the definition in the context of Title 31 only.  Wherever "Private road" is used in Title 31, it must be understood as defined here  (e.g. 31-17-5).  There is a priori no connection between a physical sign and what is used in Title 31.
Note that the location of the sign approximately coincides with the limit of parcel 135-3...  which is owned by the Town of Bristol.  As such, the section of the road on Town land should not be designated as private.  Further down, the road crosses into land owned by the Pokanoket tribe (#135-2).  It is possible that this section is inaccessible to the public.
I am not a lawyer but I wish we had more clarity here.

Thanks.