Little concrete obelisks—BERy/MTA related?

I've now found two of these, both about four feet tall—one on Mass Ave in Cambridge, and one on Belmont Street in Belmont. Can't make heads or tails of them. The one in Cambridge says 1951 on one side. Both have holes that look like something was mounted on them. Are these transit vestiges?

I recall years ago seeing small public mailboxs mounted on posts such as these, usually in less populated residential neighborhoods. The spacing of the holes is about right. These were used before the vastly larger ground mounted mailboxes became more widespread. Maybe these are remants of those?

Yep, that's it! I had a feeling that even if it was not transit related, someone here would know what it really was. Thank you for the help.

http://forgotten-ny.com/1999/12/ancient-mailboxes/" onclick="window.open(this.href);return false;