I've tried printenv, whoami, and uname to see if the "GJThinkPad" string is located in any of them. It is not.
I've also checked to see if there is a ~/.bash_profile file which might have modified the command prompt default. No such file exists.
I'm searching for other sources from which this value might have arrived. It did not used to be there, and seems fishy.
Suggestions on where to search next?
There's really nothing fishy about it.
Your computer tries to determine its own name automatically. This is perfectly normal. It does so by contacting servers on your local network and, depending on your specific network setup, remote servers typically hosted by your internet service provider.
It is very common for home and small business ISPs to give out IP addresses to their customers in a dynamic way (i.e. every time your home "modem" connects to the ISP and periodically, it could be given a new, seemingly random IP from their pool of addresses).
An IP address usually has a name given to it (determined by a so called "reverse lookup" in DNS). For home users this is all typically handled by their ISP. It's usually not something the ISP pays much attention to at all. It is very common to just see the names being listed as "dynA_B_C_D" (with the capital letters being the IP address) or similar.
In your case, they had the name "GJThinkPad" listed for your IP at the time.
It's not a problem, it's not fishy. You can rename your computer if you want to avoid seeing "GJThinkPad".
