A Signature Pokémon is the most trusted Pokémon that a trainer has. Typically a trainer only has one Signature Pokémon (though there are instances of two or more), since they are considered to be the strongest on their team. Most Gym Leaders, Elite Four, and anime characters all have one, (such as Ash's Pikachu, or Lt. Surge's Raichu). Trainers tend to save their signature Pokémon for last, since it is the strongest on their team, and are often highly associated with the character.
In the Games
Kanto
Gym Leaders
Brock - Brock's Onix
Reward:
1BP
Misty - Misty's Starmie
Reward:
1BP
Lt. Surge - Lt. Surge's Raichu
Reward:
1BP
Erika - Vileplume
Reward:
1BP
Koga - Weezing
Reward:
$ 4300
Janine - Venomoth
Reward:
1BP
Sabrina - Alakazam
Reward:
1BP
Blaine - Arcanine
Reward:
1BP
Giovanni - Rhyperior
Reward:
1BP
Elite Four
Lorelei - Jynx and/or Lapras
Reward:
$ 6600
Reward:
$ 6800
Reward:
$ 7000
Reward:
1BP
Reward:
$ 11520
Johto
Gym Leader
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Elite Four
Reward:
$ 7440
Reward:
$ 7740
Reward:
$ 7680
Reward:
$ 7680
Team Rocket
Reward:
$ 1200
Reward:
$ 1320
Reward:
$ 2560
Reward:
$ 3040
Notable Trainers
Reward:
$ 3840
Reward:
$ 3240
Hoenn
Gym Leader
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Reward:
1BP
Elite Four
Reward:
$ 4900
Reward:
$ 5100
Reward:
$ 5300
Reward:
$ 5500
Reward:
1BP
Reward:
1BP
Team Magma
Reward:
$ 1920
Reward:
$ 1320
Reward:
$ 3120
Team Aqua
Reward:
$ 1360
Reward:
$ 1720
Reward:
$ 3440
Battle Frontier
Reward:
18BP
Reward:
16BP
Reward:
16BP
Reward:
20BP
Reward:
15BP
Reward:
13BP
Noland has no signature pokemon.
Notable Trainers
Reward:
3420
Reward:
$ 2740
Reward:
$ 2740
Sinnoh
Gym Leaders
Roark - Rampardos
Reward:
1BP
Gardenia - Roserade
Reward:
1BP
Maylene - Lucario
Reward:
1BP
Crasher Wake - Floatzel
Reward:
1BP
Fantina - Mismagius
Reward:
1BP
Byron - Bastiodon
Reward:
1BP
Candice - Froslass
Reward:
1BP
Volkner - Electivire
Reward:
1BP
Elite Four
Aaron - Drapion
What's interesting to note about Aaron's signature pokemon is that it is not actually a bug type (like the rest of Aaron's pokemon), rather it is evolved from a bug type.
Bertha - Rhyperior
Flint - Magmortar
Lucian - Unknown, potentially Bronzong or Gallade
Cynthia - Garchomp
Team Galactic
Mars
Jupiter
Saturn
Cyrus
Battle Frontier
Notable Trainers
Barry
Dawn or Lucas
Unova
Gym Leaders
Cilan
Cress
Chili
Elite Four
Marshal
Team Plasma
Colress
Ex-Team Plasma
N - Zekrom (Black/Black 2) or Reshiram (White/White 2)
Notable Trainers
Hugh
Bianca
Kalos
Gym Leaders
Viola
Elite Four
Wikstrom
Team Flare
Aliana
Notable Trainers
Emma
Calem or Serena
International
Looker :
Red - Red's Pikachu
Reward:
1BP