In general, they all mean that a product

UL: Underwriters Laboratories Inc.

ETL: Originally a mark of ETL Testing Laboratories, now a mark of Intertek Testing Services

FCC: Federal Communications Commission

Although these logos share the same meaning that a certified product has passed certain safety standard, there are still many differences. Let me take HOLSEM products as an example and explain. If you look at the back panel of a HOLSEM product, you will see a well-marked certification label with logos such as UL, ETL, FCC and etc.