what command to use to create section arrows better still with letters ?
You could use Arrowhead and stick them on the ends of a polyline. However arrowheads are screen space objects and do not scale with the zoom level, which is probably not good for you. So, I might use a Leader object from the arrowhead tip location to the midpoint of the section indicator (without text), then Mirror it and group the two (you can’t “join” dimensions).
Leader object with no text it is then,
maybe we could have a section arrow command created by someone.