Here are some recent photos.
The totem pole is outside a Jamaica Plain (JP) coffee shop, where on certain days, people pay for the next person’s coffee. When I took my turn to “pay it forward,” the puzzled recipient said, “Gosh, I love JP.”
Next is a Red Line ball on High Street in Boston. Steve Annear reports at the Boston Globe that Lars-Erik Fisk “used polycarbonate to shape the sculpture before he added a windshield, destination arrival sign, and headlights and tail lights to the sphere to capture the T’s look.” (Fisk also made the Green Monster inside the building.)
The second sculpture is on Franklin Street. The giant tree mural is on a Congress Street parking garage, near Government Center. The beautiful staircase is at the Massachusetts State House.
The Redcoat is at the North Bridge, as is the bittersweet on the gate. The dogwood and the Japanese Maple are at my house.
Suzanne's Mom's Blog 
Those sculptures are wonderful–I love the red ball! What gives with the sign about the hollow sidewalk?!
I was hoping somebody knowledgeable about sidewalks would answer that question. In any case, I suppose it keeps people from trying to park on it.