There is a thread below talking about some of the security features on Paulson chips, the micro-dot, the clear plug and the bar code. Here is one that I discovered a long time ago that I haven't seen on any other chip since. Have you seen it anywhere else? If so, I'd like to know.

This is the Grand Opening chip from Harrah's in Joliet, IL. It was released in mid 1993. The photo of the boat on each side of the chip appears to be the same. When you use a magnifying glass though you can see they have done some microprinting on one side around the Harrah's logo on the "Grand Opening" side of the chip. This printing is invisible to the naked eye.