as a rule, switches in yards had a target or lamp atop the switch stand that indicated which way the switch was lined. most of what i saw in the 60's and 70's were a green indication for the main or normal route and yellow for the diverting route. keeping the lamps filled with oil and lit became something of a problem so most railroads did away with them and depended on reflective targets instead. i would think the lamps were common during the era you mentioned and would be more so the earlier era you model.
where yard tracks entered the main line there were several methods of signalling. as best i can remember, they were as follows.
if the switch was thrown remotely by a block operator, you would usually find a dwarf or pot signal controlling movements out of the yard track and on to the main.
sometimes, the operator had to unlock the switch electrically so the yard crew could throw it manually. this circuit was often on a time delay and the clock would have to run down a predetermined length of time before the switch would unlock. this prevented lining a switch wrong in the face of an oncoming train.
often, there was just a high switch stand with a light or target atop it and it was strictly a manual operation although a crew member would call the block operator and ask for permission to use the main before he unlocked and threw the switch. this communication was facilitated by using a telephone on a pole near the switch. the same phone was used to report in the clear when a movement was made from the main into the yard. often, these manually thrown switches were interlocked to the signal system on the main line and lineside signals on the main would give a restrictive indication to notify trains that a switch was open somewhere in the block.
grizlump