Not a stamp collector, but I posted this image, left, on another social media platform the other day. We weren’t voting by mail in 1964 but there was a strong movement to register in the US during that decade.
In some places, a citizen can yet register to vote. In my state, you can do it on Election Day itself. But I recommend doing it ahead of time to lighten the lines at the vote centers.
If you are choosing the mail route, and use this stamp pictured here, be sure to add a fifty-cent stamp to make sure it gets where it needs to go to be counted.