Approved artists painting TSBs this year may be painting newly installed cabinets. New cabinets have 'light sensors' fitted below the lid of the TSB. The 'light sensors' measure the available light at the intersection and adjust the brightness of the traffic lights.
Clearly the 'light sensor' cannot do its job if it there is paint on it. Please Click_Here to see where the sensors are located on the new TSBs.
Please take care not to paint it. Thank you :)