Reddit users went into a spin on Monday after a sleuth discovered that shining a UV light on Aussie banknotes revealed hidden images of birds.

Reddit user C_Horse21 made the discovery with a $100 note and shared it online, quickly racking up over 2400 and setting off a frenzy in the comments.

one user said, decrying the lack of National Treasure-styled secrets on the iconic US greenback.

said another.

Every Australian banknote includes three features - a bird, serial number and year of print - created using fluorescent inks.

Each note has a different bird: the eastern spinebill honeyeater ($5), cockatoo ($10), kookaburra ($20), black swan ($50) and owl ($100).

While the hidden bird may have prompted a wave of conspiracy-like excitement, it's actually one of several unique security measures built into the design of our notes to combat forgery.

Read on for a detailed list of what other Easter eggs are contained on the loose fiver sitting in your pocket, as well as how to spot a fake.

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Secret images hidden on your cash revealed(https://www.news.com.au/finance/money/wealth/secret-images-hidden-on-your-cash-revealed/news-story/bcd54d8360b3f2fce3b9542a6eb0fb60)