Signature Move

A Signature Move is any move that is learned by only one or a few Pokémon, making it unique. Examples of signature moves are Volt Tackle, which is only learned by Pichu, and Chatter which is only learned by Chatot. Every signature move can be learned by at least 12 Pokémon: The Pokémon it is known by, Ditto when using Transform, Mew using Transform or Metronome, Smeargle by using Sketch, some by Mimic, and the rest by using Metronome.

Examples
Pichu = Volt Tackle

Jynx = Loveley Kiss

Dialga = Roar of Time

Palkia = Spacial Rend

Rhyperior = Rock Wrecker

Zangoose = Crush Claw

Seviper = Poison Tail

Chatot =Chatter

Blaziken = Blaze Kick

Swampert = Muddy Water

Giratina = Shadow Force

Arceus = Judgement

Shaymin = Seed Flare

Lugia = Aeroblast

Hariyama = Arm Thrust

Vespiquen = Attack Order, Defend Order, Heal Order

Weavile = Beat Up

Marowak = Bone Club, Bonemerang

Porygon = Conversion, Conversion 2, Sharpen

Regigigas = Crush Grip

Darkrai = Dark Void

Jirachi = Doom Desire

Alakazam = Kinesis

Cresselia = Lunar Dance

Latios = Luster Purge

Miltank = Milk Drink

Latias = Mist Ball

Cacturne, Cacnea = Needle Arm

Octillery = Octazooka

Meowth, Persian = Pay Day

Deoxys = Psycho Boost

Ho-oh = Sacred Fire

Smeargle = Sketch

Chansey, Blissey = Softboiled

Oshawott, Dewott, Samurott = Shell Sword

Zorua, Zoroark = Night Daze

Keldeo, Cobalion, Terrakion, Virizion = Sacred Sword, Secret Sword

Zekrom = Fusion Bolt, Bolt Strike

Reshiram = Fusion Flare, Blue Flare

Kyurem = Cold Flare, Freeze Bolt, Glaciate

Delibird = Present

Victini = V-Create, Searing Shot