Stickers were a new feature introduced in Pokémon GO Version 0.177.0. These allowed for you to attach stickers to the Gifts that you send to other people. These stickers are all aesthetic and don't provide any benefits.

You can get stickers by opening gifts and through purchasing them in the Pokémon GO Shop.

Pokémon GO Stickerss

List of Stickers

Pumpkin Pumpkin Gifts at Halloween
Costume Sableye Costume Sableye Gifts at Halloween
Costume Squirtle Costume Squirtle Gifts at Halloween
Costume Pikachu Costume Pikachu Gifts at Halloween
Costume Charmander Costume Charmander Gifts at Halloween
Costume Bulbasaur Costume Bulbasaur Gifts at Halloween
Costume Gengar Costume Gengar Gifts at Halloween
Sierra Sierra GO Rocket Leader Battles
Cliff Cliff GO Rocket Leader Battles
Arlo Arlo GO Rocket Leader Battles
Slowbro Slowbro Gift
Alolan Meowth Alolan Meowth Gift
Slowpoke (nagano) Slowpoke (nagano) Gift
Marill (nagano) Marill (nagano) Gift
Gift Gift Gift
Oshawott Oshawott Gift
Pikachu Pikachu Gift
Mudkip Mudkip Gift
Torchic Torchic Gift
Treecko Treecko Gift
Victini Victini Event
GO Fest 2020 Logo GO Fest 2020 Logo Event
GO Fest 2020 Logo GO Fest 2020 Logo Event
GO Fest 2019 Logo GO Fest 2019 Logo Event
GO Fest 2018 Logo GO Fest 2018 Logo Event
GO Fest 2017 Logo GO Fest 2017 Logo Event
Niantic Logo Niantic Logo Event
Pikachu Pikachu Gift
Pikachu Pikachu Gift
Pikachu (nagano) Pikachu (nagano) Gift
Pikachu & Raichu (nagano) Pikachu & Raichu (nagano) Gift
Ditto Ditto Gift
Squirtle Squirtle Gift
Charmander Charmander Gift
Bulbasaur Bulbasaur Gift