I have seen references over the years to a group of plastic chips from Harrah's Reno/Tahoe being bus chips. I found the box below at an antique show a couple of weeks ago, which shows one of the four chips in question. The box was filled with these plastic chips of various colors. I continue to maintain that these specific chips were souvenirs and made for home use.

Here is the current listing from the chip guide:

CG045887 - BEIGE - Shown
CG045888 - NAVY They were given out to Harrah's customers
CG045889 - RED They were given out to Harrah's customer
CG045890 - YELLOW They were given out to Harrah's customer

Chips were given out to Harrah's customers to be use as "bus tokens" as a marketing ploy to get more people to their casino during the early years at Lake Tahoe