Complex sentence: As a part of The Smartest Card campaign, every September public libraries celebrate library card sign-up month, where the library card is promoted as the most important card that people have in their wallet.
Split into simpler sentences: As a part of The Smartest Card campaign, every September public libraries celebrate library card sign-up month. During Library Card Sign-up Month, the library card is frequently promoted as the most important card that an individual can have in their wallet.