They are marked 0, +2, +4 etc
What do they signify?
Thanks in advance
They are the bonus to the points you score for spinning gyrodynes in the production phase at the end of the round.
For example if you have 2 gyrodynes spinning valued 1 & 2. You would score a total of 7 points if the bonus was +2.
If the bonus is +? the bonus is the median value of the dice for that round (rounded up).