The first picture shows the current draw on 6 volts for a good field winding.
The second picture shows polarity of the fields.
The third picture shows how residual magnetism will still make the north needle of a compass point to the left field when the brush end is UP and the terminal is AWAY from you.
If you hold the compass on the outside of the case the south end of the needle should be pointing to the left field. Remember you have a coil of wire wound a certain direction and current passing a certain direction to make the left coil NORTH on the inside, so the other end of that coil would be SOUTH.
If there is any doubt, which there obviously is, or you wouldn't be asking, just pick up a cheap compass and try this check.