To find clues as to when the building was built that obsured this sign, I started looking for old photos of the 15 Elm St. Savers Bank Building. 

1960s ? view of the building which covered the sign

Text on  p. 21 of Sesquicentennial book last paragraph

 “The bank’s move to the Lenti Building in 1938 was followed in 1951 by the purchase of the building at 15 Elm St.” 
- provided by Margaret Morrissey (Jacob Edwards Library Director)

Therefore, we can assume the building predates 1951.

At present, the oldest photo I have found was taken by my father Don Whitney in 1954.
Here you can clearly see the building to the right of the gulf sign, with the Maci building in the background.