I recall seeing a LOT of clock radios from the 60's and 70's that used those flip number mechanisms. Of course the Telechron clocks predate these and were often found on TV sets and in Ham radio shacks (of course these were considered pretty high tech in thee day although I doubt they were any more accurate than a typical clock).

I believe the neon tube clock that someone mentioned to be equipped with Nixie tubes. These were alpha-numeric displays which means that they could actually show both numbers and letters (and some symbols too). There are tons of really cool sites all about these tubes as well as digital clocks in general. Do a Google.

Anthony