I sometimes see letters next to a Pokémon when I encounter what do they mean? I recently encountered a Pokémon (don't remember the name) and it had "(J)". What does that mean?
That denotes what region they are from. So "S" means "Sinnoh" while "J" means "Johto" and so on. That just tells you what Pokémon you have (for example, if an Eevee with a "S" tells you what Eeveelution it will become). Hope this helps.
WHAT!? I encountered an eevee with a U!...I didn't have any pokeballs! Waaahhh!! I missed out on a future umbreon :-:
An Umbreon or Espeon would be an Eevee (J) since those are from Johto. Unova did not introduce any eeveelutions so there shouldn't be an Eevee (U) in the catcher.