I guess they could have a USB certification body, kinda like UL is for wall power devices, and require that a device have an certification ID number on it that you could look up in their online database to qualify. I mean, you could forge a fake number that doesn't map to anything, but I feel like that's a higher bar than just throwing a USB symbol on there. Like, you gotta know that you're doing something fraudulent in that case.

investigates

Huh.

Apparently UL does certify USB devices. I have no idea how to tell whether a UL-marked device of a given age is certified to do what from the logo alone, though. I guess you could look it up with UL.

https://www.ul.com/services/ul-taiwan-usb-test-lab

I bet that only my high-power USB chargers have it, though. Honestly, I didn't even know that they covered USB, wouldn't have looked for a UL mark on USB devices.

investigates

Well, my Logitech F710 gamepad does have a UL mark. That's some proprietary wireless protocol, uses AA batteries. Not USB and doesn't plug into the wall. Dunno whether they certified it for wireless or power safety or whatever.

looks further

I have a wired USB gamepad with a bunch of Chinese characters, the URL "www.izdtech.com", no USB labels, and no UL mark.

I have a wired/wireless USB 8Bitdo gamepad with a CE mark, USB symbols, and no UL mark (I understand that CE doesn't work like UL. It doesn't indicate that any independent organization has tested the device, just is a concise way to state that the device manufacturer states that the device conforms to some set of standards).

I have a 100W USB PD "Nekteck" charger with a UL mark and some ID number that looks to be associated with that, no CE mark, an FCC mark that I assume is related to RF interference compliance, an enormous USB standard mark with the 100 watt capability listed, and some sort of mark with a box inside another box that I don't recognize.

I have an SIIG USB audio interface that has no USB labels, a CE mark, an FCC mark, and no UL mark.

I have a USB-powered audio mixer that has no USB labels, no FCC mark, no UL mark and a CE mark.

I have a laptop USB charger that has no USB labels, a CE mark, multiple UL marks, one of which appears to be in some sort of teardrop-looking thing, some "UK CA" mark that I assume is some kind of UK regulatory body. It's got that same mysterious "box in a box" mark that I saw before, "VI" in a circle, a picture of a house, some "NYCE" mark, and a "NOM" mark.

I bet that most people have basically no idea what any of this means. I probably know what more of it means than the average person, but definitely not enough to extract a whole lot of information from this. And all of these have a different set of marks; there is no least-common-denominator mark.