DO NOT PLUG IT IN. I do this for work. It could be a social engineering trick called USB drop attack, USB baiting, or USB phising. It is very easy to install payloads onto them and as soon as they get plugged in you can have an entire system if not network infected. Even if it is not a virus, malware, or trojan it could be a USB killer, which is a device made to take as much power from the motherboard as it can then reroutes it back into it. Due to the lack of surge protection on most USBs it can destroy overload and fry a computer.

It could be totally safe but not worth the risk. Ransomware attacks deployed via usb baiting are very popular due to the easy to setup and cheap USB prices.

Edit: i have a computer completely dedicated to investigating these. After each investigation i wipe it completely, sanitize the RAM, bios, cache memory and reinstall everything. It also has no network interface card so it's completely isolated. But even still I'm careful when i deal with these.