I remember this Phonebox Adverts for Years. This one from the Yazoo Milkshake Product has stuck with me where its a Yellow Superhero Suit with Purple Cape, Overpants and Boots plus a Y logo on the Chest and Belt Buckle.
with the Subtext: Save Your Imagination.

I've modified this one so that the Y logo on the Chest is in a Circle. There is a Character who wears it but Who?

Yazoo Superhero Costume ©: Yazoo Milkshake Product