Hamilton ceased production in the US in 1969 and moved production to their factory in Switzerland that they acquired years earlier.
I imagine that as the end neared there was an inventory of US-made movements like the 770, 736 and 731 calibers and Hamilton product managers had to decide what to do with them.
Several models were created and one of the best known is the Liberty Coin. It was not catalogued and there are no precise production figures but common estimates are under 500, which makes the Liberty Coin one of the rarest models produced. It was offered in 14K solid gold as well as 10K rolled gold plate (RGP), the latter being more common.
One of the interesting aspects of the Liberty Coin is the minor variations you'll find. Some examples have black baton hands while others have black dauphine hands. The crowns used also seem to vary. Interestingly, the model does not have a second hand - just the hour and minute hand. That's very unusual and did they do that because the 4th wheels had bent pivots (so they just removed them)? Also of interest, the Liberty Coin is one of the only authentic models to promote the number of jewels on the dial. The only other models that did that are the other models I believe were produced at the same time, like this diamond-dialed version that you'll find in both yellow and white RGP cases.
I posted on the Liberty Coin 10 years ago and I recently had the opportunity to work on another so I thought I'd show it again.
As received, it is very similar to my earlier example however this one has dauphine hands and an unusually thin crown.