Two and three head masts indicate speed and route at turnouts (particularly at the points) as in this interlocking ...
?
?
Approaching the frog may be a single head mast or dwarf if simple main or entry to main.
Track configuration beyond the turnout might be multiple head if there are other elements or routes.
One on my prototype had a double headed mast on simple entry to the main (at one time, there was a passenger station beyond).
--
Ken
NYNH&H, Old Colony Division, Cape Cod Branch (1949-1959)
Loconet * JMRI 5.9.3 * OSX,Win10,Ubuntu
Blog: ?
Ken Heywood