An early example of this is reverse of the Great Seal of the United States, included on the dollar bill, with its famous pyramid and all-seeing eye. I suppose we can forgive this, as I doubt that 18th Century designer Pierre Eugene du Simitiere could have predicted the popularity of Masonic conspiracy theories in 21st Century America.
Entering the computer age, we have the bar code. I'm convined that George Laurer deliberately designed the three control bars at the beginning, middle and end of a UPC barcode to resemble the bars that represent the barcode number six. What better way to scare the Beejesus out of a certain type of evangelical Christian than to encode the Mark of the Beast into their groceries?
Which brings us to the modern day. I recently moved house and had to get a new UK photocard driving licence. When it turned up in the mail, I noticed the design had changed slightly. Being a nerd, I examined it noticing that it had a new holographic anti-fraud feature. I tilted the card to look at the hologram design: a steering wheel which turns as you tilt the card. Cute. But, hang on, what's that in the background? A pyramid! A pyramid with rays eminating from it as they do from the all-seeing-eye in the pyramid on the dollar bill!
Someone, somewhere is chuckling to themselves at their successful inclusion of this symbol in the UK driving licence. When the first website goes up declaiming the use of this "illuminati" symbol on the photocard, designers will drink a toast to another successful wind-up.