I was taking this photo for my stock photo files when a passerby asked, "Can they do that?"
Yes, the parking enforcement officers can and do stack Boston parking tickets.
Here's the law from the city's website:
"Section 17. Multiple Parking Tickets-What Constitutes a Separate Violation
1. A vehicle which has been issued a parking ticket in accordance with Section 13B of Chapter 190 of the Acts of 1982 and these regulations, and has not been moved in the interim, may not be issued a second parking ticket for six (6) hours, with the following exceptions:
a. If the parking regulations at a particular location change due to time, then a second parking ticket may be issued after the expiration of ten (10) minutes from the time the first parking ticket was issued.
b. Parking tickets issued for stopping, standing or parking in violation of Article IV, Section 1, Part 24 (no valid registration plate), Part 25 (no valid certificate of inspection) and Part 26 (performing non-emergency repairs to a vehicle) may be issued independently of parking tickets issued for a violation of any other regulation.
c. Parking tickets issued for stopping, standing or parking in violation of Article IV, Section 4, Part 5 (parking beyond the time limit indicated on the parking meter)."
You can download a complete PDF of parking regulations here.