What do the rock, paper, scissors icons mean in Pocket Mortys?

The rock, paper, scissors icon displayed next to a Pocket Mortys' name is a much simpler version of the Pokémon class system, such as water or rock type Pokémon. You can use these icons to gain an advantage over your opponents.

For example, a Rock type Morty will do much better against a Scissors Morty, Scissors Mortys have an advantage over Paper Mortys, and so on. The only Morty that does not have a type is the original Morty you begin the game with.