At the end of season 3, the rangers (and the world) had time turned back, and they became children.
In order to protect the Earth, Zordon enlisted the Alien Rangers of Aquitar to help.
These alien rangers used coins to summon their Zords.
Based upon Kakuranger, these coins used the symbols from the Doron Changer.
I was able to get one for a reasonable price, so I made Alien Ranger coins that fit in the Mighty Morphin Morpher.