A page from the 1977 MBTA Standards Manual showing the specifications for a map panel as installed at the entrance level of a station, using Kendall inbound as an example. Signage much like this can still be seen across most of the rapid transit network.
Interestingly, there’s no Kickstarter campaign to reissue this particular standards manual, perhaps because it wasn’t created by a famed Italian modernist designer and is typeset in the most basic manner possible, but there’s no shortage of fascinating information available in it: the PANTONE colours used for each of the rapid transit lines, for example, or why there’s no Yellow Line (the colour was reserved for bus services). Best of all, the PDFs are available for download from the MBTA’s website (Part 2 contains the graphics standards pages if that’s all you’re interested in).