I am reading the paper "The Blockchain Folk Theorem" by Biais et al (2019) (http://publications.ut-capitole.fr/26234/1/32/5/1662/5427771). It is a stochastic game and the authors include a sunspot random variable to "enable players to coordinate their actions using a public randomization device". I went around and tried to look more into this and I couldn't really find any intuitive explanation for what a public randomization device is (there seems to be some information on the mathematical properties of including such a device, specifically the authors reference a paper on noisy stochastic games by Duggan (2012) (https://onlinelibrary.wiley.com/doi/abs/10.3982/ECTA10125)).
I guess my question is, could anyone here provide some explanation of this concept? Or even just some reference to better understanding the concept of public randomization devices?