Bell in No. 9's cab?

I note WW&F 9 has a gong-type bell on the ceiling of the cab. Our CVR 4-6-0 220 has a similar gong bell mounted to the front cab wall, that none of the old CV guys I worked with knew the purpose of, though one suggested it may have predated the signal line air whistle system. Others have suggested it may have had a rope going forward to a snowplow being pushed, to communicate between the crews. While using a 69" drivered passenger engine to push a snowplow seems unlikely, No. 220 does have a front headlight connection as would be used for such purpose. Thus, I'm wondering what the real purpose of these gong-type bells actually was?