The Mayans were interested in Venus itself, not necessarily in transits of Venus. I don't believe there is a record of Mayans observing a transit, although they might have known that a transit could occur, because they were so familiar with the motions (and thefore the orbit) of Venus. One way it might have been possible (but dangerous) to observe a transit, would be if the transit happened at sunrise or sunset. At that time, if conditions were right, clouds could allow an observer to see Venus crossing the disk of the Sun. This is something that NO ONE should try today, because if the cloud cover is not "just right" you could go blind.