Thunderbolt cables should also have a lightning bolt icon on the connector.
As far as any cables wtihout markings on the connector, then check the wire sheathing....sometimes there may be some sort of designation written there although it can be extremely hard to see. No matter what, unmarked cables are most likely only supporting the USB protocol, but which protocol & speed? No way to know without testing. FYI, Apple's USB-C charging cable is only capable of USB2 speeds. Some USB-C cables may not even support any Thunderbolt or USB protocols, and may instead just be out right basic charging cables.
Probably best to label each cable you receive with your devices to know what they are & where they came from. Many times cables provided by a manufacturer with their device is not always a good quality cable.