I think this thread here pretty well covers them all:
http://forum.mikrotik.com/viewtopic.php?f=3&t=38741
The general rule that gets me by, look at the silk screening, there is usually "J" or "ANT" followed by a number next to each antenna connector. Whichever is the lower of the two is the primary chain. For example, if the two jacks are labeled "J3" and "J4", then J3 is chain-0 (Primary antenna), and J4 is chain-1.