It is PRIMARILY a reminder and a CONTROL MECHANISM
That is just nonsense, I'm afraid. Sure, the evidence was initially equivocal, but lots of studies suggest they do have a statistically significant impact in reducing spread, particularly in confined indoor spaces.
https://www.nature.com/articles/d41586-020-02801-8
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497125/
https://www.pnas.org/content/118/4/e2014564118