There are three ways we can try to explain this sign. Purgatory is either a pit-stop on the way to heaven, the process of flushing your insides out, or a settlement in La Plata, Colorado named for a river where Spanish explorers died in 1776. We wonder whether they drank the local water to celebrate discovering silver but that’s pure speculation too.
When prospectors followed in search of lodes of silver they had to pay a 50c toll to cross a farmer’s land to get there. Those without the correct change were gridlocked at the toll booth, where they could only dream of leaving Purgatory on the way to their heavenly bonanza.